Accurate Radiographic Calibration Using Multiple Images

ABSTRACT

A radiographic system may be configured to capture a first radiograph containing a first image of an object with the source and the receiver in a first orientation with respect to one another. The system may store the first radiograph and metadata representing vertical and horizontal positions of the first orientation. At least one of the source and the receiver may be moved so that the source and the receiver are in a second orientation with respect to one another. A second radiograph containing a second image of the object may be captured with the source and the receiver in the second orientation. The second radiograph may be stored in memory along with metadata representing vertical and horizontal positions of the second orientation. Based on the captured radiographs, a magnification of the object of interest, as represented by the first image or the second image, may be determined.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of and claims priority to U.S.patent application Ser. No. 15/205,880 filed on Jul. 8, 2016 andentitled “Marker Positioning Apparatus,” which is a continuation-in-partof and claims priority to U.S. patent application Ser. No. 14/989,437filed on Jan. 6, 2016 and entitled “Accurate Radiographic CalibrationUsing Multiple Images,” each of which is herein incorporated byreference as if fully set forth in this description.

BACKGROUND

Orthopedic joint replacement surgeries such as hip replacement and kneereplacement typically involve replacing a damaged bone or joint with aprosthetic implant. Similarly, orthopedic stabilization surgeriesinvolve bracing or fixating an injured bone so that it heals properly.The prosthetic implant or brace is shaped in a way that allows movementsimilar to that of a healthy joint.

In order for an orthopedic replacement procedure to be successful, aphysician anticipates both the size and shape of the prosthetic implantthat will most closely match the anatomy of the patient. This is oftendone based on radiographic (i.e., X-ray) images of the patient's jointand the associated bone structure. If the size and shape are estimatedincorrectly, the necessary prosthetic implant might be unavailableduring surgery. A prosthesis of incorrect size might be implanted,leading to complications.

SUMMARY

In the field of medicine, it is often useful to identify themagnification of an object or objects (e.g., blood vessels, tumors,bones, hardware implants) within a radiograph or a representation of aradiograph. Knowing the magnification of different body parts within aradiograph enables medical professionals to determine their actualphysical size.

For example, in orthopedic surgery, medical professionals often measurethe size of multiple objects including hardware implants, bones, jointsand bone lesions. This enables the medical professional to determine: 1)if a bone lesion has changed in size, 2) a fracture has significantlydisplaced, or 3) what type and size of hardware is required toreconstruct a joint, a bone, or stabilize a fracture.

In order for an orthopedic replacement procedure to be successful, aphysician may need to anticipate both the size and shape of theprosthetic implant that will most closely match the anatomy of apatient. Traditionally, the physician may manually size implants basedon radiographs of the patient's joint and the associated bone structure.The physician may place a clear sheet, called a template, containing anoutline in the size and shape of the prosthetic implant over theradiograph. The template may include anatomical reference markings.Given that radiographs and the images contained therein are typicallymagnified by approximately 10% to 25%, the template is also typicallymagnified to account for the anticipated magnification of the patient'sbone structure when a radiograph is taken.

Using multiple templates in a trial-and-error fashion, the physician mayeventually select a size for the prosthetic implant. However, asdifferent anatomical features of a joint are located at differentheights, they are magnified to a different extent. Additionally,radiographic magnification also varies among people with different bodyhabitus (e.g., obese, very muscular). Unfortunately, the traditionaltemplating process only approximates the magnification for theradiograph and assumes that this approximation applies equally to allanatomical features depicted in the radiograph. As a result, thetraditional approach may result in the selection of a prosthetic implantof the wrong size.

In order to overcome this problem, some physicians place a sizing markeron the radiograph that enables them to more accurately determine themagnification of the radiograph and the images contained therein. Oncethe radiograph has been templated, the physician then adjusts theselected prosthesis size by the determined magnification. However, sincethe template is not resized to the correct magnification prior to beingplaced over the radiograph, the incorrectly sized template can be placedin the incorrect position. Accordingly, using a sizing marker does notimprove the accuracy of the templating process.

With the introduction of digital imaging, traditional templating isbeing replaced by digital templating. With digital templating, thephysician views a representation of the radiograph on a computer anduses a digital representation of the template to select a replacementprosthesis closest in size and shape to the anatomical features of thepatient. Digital templating has a significant advantage over traditionalmethods in that digital templates are not limited to one sizemagnification. Templating software enables either the templates or theradiograph to be adjusted to the correct magnification prior toplacement of the template. However, digital templating still has onemajor weakness. Namely, it does not have a reliable and reproduciblemethod of determining the magnification of an object image or objectimages within a radiograph. As a result, despite the advantages ofsoftware, it is often just as inaccurate as templating using traditionaltemplate overlays.

To determine the magnification of an object image within a radiograph, acalibration process is required that precisely determines the height ofthat object above a radiographic receiver at the time when theradiograph was obtained. Unfortunately, as described below, existingmethods are not reliable as some of them depend on marker placement by amedical professional at an estimated height of an object deep within thehuman body. Not only is this method fraught with human error, the erroris not readily identifiable while a user is templating the object imagewithin the radiograph. Thus, the user might not know if the templatingresults are accurate.

Additional weaknesses exist with current methods of calibration. Presentmethods of calibration apply the same scaling factor to all objectimages within a radiograph as they do not have a way of determining theheight of different objects of interest depicted within a radiograph. Asa result, multiple objects cannot be templated accurately as they areoften at different heights than the calibration marker.

Finally, when only a single magnification factor is applied across theentire radiograph, additional information such as the rotationalposition of an object depicted within the radiograph cannot bedetermined. Since joint and bone rotation often determine the shape oftemplate chosen, without knowing the rotation of the joint at the timethe radiograph was taken, the selected prosthetic implant often does notaccurately reflect the anatomy of the patient's joint.

Health care providers (e.g., hardware manufacturers, hospital systems,and medical professionals) have attempted to leverage the preoperativemeasurement capabilities of digital templating to reduce the cost ofcare and improve patient outcomes. In particular, accurately determiningthe size of a bone or joint prior to surgery may improve patientoutcomes and reduce the cost of supplying medical hardware to theoperating room by narrowing the range of hardware that needs to beavailable on-hand during surgery. Manufacturers of the medical hardwaremay consequently produce, transport, and store less hardware. Likewise,hospital systems may keep fewer products on the shelf and may reducesurgical cost associated with preoperative hardware management andoperative time. Additionally, accurate preoperative measurements mayreduce surgical time and facilitate a significant reduction in operativecomplications by providing hardware that most closely matches the sizeand shape of a patent's anatomical features.

Determining the actual physical size of a patient's anatomical features(e.g., bones and bone features) may be of notable importance in acost-conscious medical environment for additional reasons. Inparticular, as hospital systems attempt to reduce costs by decreasingthe hardware and accessories available off the shelf in the operatingroom, the correct hardware may be unavailable intraoperatively if thesize and shape of the patient's anatomical features were not accuratelydetermined prior to surgery. Similarly, if a patient has abnormallysized joints or is an unusual variant with respect to body composition,off-the-shelf hardware may not match the patient's anatomy and thepatient may require customized replacement hardware. If the size of thepatient's anatomical features is not determined accurately, thecustomized hardware may not be a good fit.

Inaccurate preoperative templating may prolong surgery and may cause asurgeon to place incorrectly sized hardware on the patient, leading tocomplications. Complications may include, but are not limited to,non-healing, chronic pain, deformity, instability, nonvascular injury,deep venous thrombosis, pulmonary embolus, infection, and/orcardiac/respiratory compromise. Additionally, surgically implanting anoversized prosthesis in a patient may result in an increased incidenceof femoral fracture, excess leg length, or nerve palsy. Conversely,hardware loosening, shortened leg length, or hip dislocation may resultfrom implanting undersized hardware.

The embodiments described herein are generally directed to determiningthe magnification of an image of an object of interest in a radiographby using at least two different radiographs, each radiograph capturedfrom a different orientation. In contrast to existing digital templatingsolutions, the example embodiments described herein are not limited toapplying the same level of magnification to images corresponding todifferent objects of interest contained within the same radiograph.Example embodiments may determine a plurality of levels ofmagnification, each corresponding to a different anatomical feature orobject of interest, the images of which may be contained within aradiograph.

Additionally, example embodiments are also directed at determining theposition and orientation of multiple objects based on at least twodifferent radiographs. For example, the embodiments described herein maybe used to determine the degree of femoral anteversion or retroversionbased on at least two different radiographs, each acquired from adifferent perspective. While prior methods might not accurately accountfor femoral rotation, the embodiments described herein enable accuratemeasurement by placing templates at a rotation that substantiallymatches the determined rotation of the femur at the time of capturingthe radiograph. As a result, no special patient positioning is required.The methods described herein are not limited to the hip and femur butmay also be used for any body part of interest.

In one example, an embodiment is provided that includes obtaining, by acomputing device, a representation of a first radiograph containing afirst image of an object of interest. The first radiograph may becaptured by a radiographic device with a radiation source and aradiation receiver in a first orientation. The embodiment also includesobtaining, by the computing device, a representation of a secondradiograph containing a second image of the object of interest. Thesecond radiograph may be captured by the radiographic device with theradiation source and the radiation receiver in a second orientation. Theembodiment additionally includes, based on a first width of the firstimage and a second width of the second image, determining a verticaldistance of the object of interest above the radiation receiver. Basedon the vertical distance of the object of interest above the radiationreceiver, the embodiment further includes determining a magnification ofthe object of interest in one of the first radiograph and/or the secondradiograph. The determined magnification may be used to scale the imageof the object of interest contained in one of the first radiographand/or the second radiograph in order to represent a physical size ofthe object of interest. The scaled image may be used to select, from aplurality of surgical templates of different sizes, a surgical templateclosest in size to the physical size of the object of interest.

In another example, a radiographic system is disclosed that includes aradiation source and a radiation receiver. At least one of the radiationsource and the radiation receiver is movable with respect to oneanother. The radiographic system also includes a processor, a memory,and program instructions stored in memory. The program instructions,when executed by the processor, cause the radiographic system to performoperations that include capturing a first radiograph containing a firstimage of an object of interest with the radiation source and theradiation receiver in a first orientation with respect to one another.The operations further include storing, in the memory, the firstradiograph and metadata representing vertical and horizontal positionsof the radiation source and the radiation receiver in the firstorientation. The operations additionally include moving at least one ofthe radiation source and the radiation receiver so that the radiationsource and the radiation receiver are in a second orientation withrespect to one another. The operations further include capturing asecond radiograph containing a second image of the object of interestwith the radiation source and the radiation receiver in the secondorientation. The operations also include storing, in the memory, thesecond radiograph and metadata representing vertical and horizontalpositions of the radiation source and the radiation receiver in thesecond orientation. Based on the captured radiographs and one or more ofthe vertical and horizontal positions of the first and secondorientations, the operations additionally include determining amagnification of the object of interest as represented by the firstimage or the second image.

A further example discloses a non-transitory computer readable mediumhaving stored thereon instructions that, when executed by a processor,cause the processor to perform operations. The operations includeobtaining a representation of a first radiograph containing a firstimage of an object of interest. The first radiograph may be captured bya radiographic device with a radiation source and a radiation receiverin a first orientation. The operations also include obtaining arepresentation of a second radiograph containing a second image of theobject of interest. The second radiograph may be captured by aradiographic device with a radiation source and a radiation receiver ina second orientation. The operations further include, based on a firstwidth of the first image, and a second width of the second image,determining a vertical distance of the object of interest above theradiation receiver. The operations yet further include determining amagnification of the object of interest in one of the first radiographor the second radiograph based on the vertical distance of the object ofinterest above the radiation receiver. Based on the determinedmagnification, the operations may also include selecting, from aplurality of template objects of different sizes, a template objectclosest in size to a physical size of the object of interest.

Another example embodiment may include a means for obtaining arepresentation of a first radiograph containing a first image of anobject of interest, where the first radiograph was captured by aradiographic device with a radiation source and a radiation receiver ina first orientation. The example embodiment may also include means forobtaining a representation of a second radiograph containing a secondimage of the object of interest, wherein the second radiograph wascaptured by the radiographic device with the radiation source and theradiation receiver in a second orientation. The embodiment mayadditionally include means for determining, based on a first width ofthe first image of the object of interest in the first radiograph, and asecond width of the second image of the object of interest in the secondradiograph, a vertical distance of the object of interest above theradiation receiver. The embodiment may further include means fordetermining, based on the vertical distance of the object of interestabove the radiation receiver, a magnification of the object of interestin one of the first radiograph or the second radiograph.

In a different example, an embodiment is provided that includeobtaining, by a computing device, a representation of a first radiographcontaining a first image of an object of interest. The first radiographmay be captured by a radiographic device with a radiation source and aradiation receiver in a first orientation. The operations also includeobtaining a representation of a second radiograph containing a secondimage of the object of interest. The second radiograph may captured by aradiographic device with a radiation source and a radiation receiver ina second orientation. The embodiment additionally includes determining afirst distance between the first image and a reference point in therepresentation of the first radiograph based on the representation ofthe first radiograph. The embodiment further includes determining asecond distance between the second image and the reference point in therepresentation of the second radiograph based on the representation ofthe second radiograph. The embodiment yet further includes determining avertical distance of the object of interest above the radiation receiverbased on the first distance and the second distance. The embodiment alsoincludes, based on the vertical distance of the object of interest abovethe radiation receiver, determining a magnification of the object ofinterest in one of the first radiograph or the second radiograph. Thedetermined magnification may be used to scale the image of the object ofinterest contained in one of the first radiograph and/or the secondradiograph in order to represent a physical size of the object ofinterest. The scaled image can be used to select, from a plurality ofsurgical templates of different sizes, a surgical template closest insize to the physical size of the object of interest.

In another example, a radiographic system is disclosed that includes aradiation source and a radiation receiver. At least one of the radiationsource and the radiation receiver is movable with respect to oneanother. The radiographic system also includes a processor, a memory,and program instructions stored in memory. The program instructions,when executed by the processor, cause the radiographic system to performoperations that include capturing a first radiograph containing a firstimage of an object of interest with the radiation source and theradiation receiver in a first orientation with respect to one another.The operations further include storing, in the memory, a representationof the first radiograph and metadata representing vertical andhorizontal positions of the radiation source and the radiation receiverin the first orientation. The operations additionally include moving atleast one of the radiation source and the radiation receiver so that theradiation source and the radiation receiver are in a second orientationwith respect to one another. The operations further include capturing asecond radiograph containing a second image of the object of interestwith the radiation source and the radiation receiver in the secondorientation. The operations also include storing, in the memory, arepresentation of the second radiograph and metadata representingvertical and horizontal positions of the radiation source and theradiation receiver in the second orientation. The operationsadditionally include determining, based on the representation of thefirst radiograph, a first distance between the first image and areference point in the representation of the first radiograph. Theoperations further include determining, based on the representation ofthe second radiograph, a second distance between the second image andthe reference point in the representation of the second radiograph.Based on the first distance, the second distance, and one or more of thevertical and horizontal positions of the first and second orientations,the operations additionally include determining a magnification of theobject of interest as represented by the first image or the secondimage.

A further example discloses a non-transitory computer readable mediumhaving stored thereon instructions that, when executed by a processor,cause the processor to perform operations. The operations includeobtaining a representation of a first radiograph containing a firstimage of an object of interest. The first radiograph may be captured bya radiographic device with a radiation source and a radiation receiverin a first orientation. The operations also include obtaining arepresentation of a second radiograph containing a second image of theobject of interest. The second radiograph may be captured by aradiographic device with a radiation source and a radiation receiver ina second orientation. The operations further include determining a firstdistance between the first image and a reference point in therepresentation of the first radiograph based on the representation ofthe first radiograph. The operations also include determining a seconddistance between the second image and the reference point in therepresentation of the second radiograph based on the representation ofthe second radiograph. The operations further include determining avertical distance of the object of interest above the radiation receiverbased on the first distance and the second distance. The operations yetfurther include, based on the vertical distance of the object ofinterest above the radiation receiver, determining a magnification ofthe object of interest in one of the first radiograph or the secondradiograph. Based on the determined magnification, the operations mayalso include selecting, from a plurality of template objects ofdifferent sizes, a template object closest in size to a physical size ofthe object of interest.

Another example embodiment includes a means for obtaining arepresentation of a first radiograph containing a first image of anobject of interest. The first radiograph may be captured by aradiographic device with a radiation source and a radiation receiver ina first orientation. The example embodiment may also include means forobtaining a representation of a second radiograph containing a secondimage of the object of interest. The second radiograph may captured by aradiographic device with a radiation source and a radiation receiver ina second orientation. The example embodiment may additionally includemeans for determining a first distance between the first image and areference point in the representation of the first radiograph based onthe representation of the first radiograph. The example embodiment mayfurther include means for determining a second distance between thesecond image and the reference point in the representation of the secondradiograph based on the representation of the second radiograph. Theexample embodiment may yet further include means for determining avertical distance of the object of interest above the radiation receiverbased on the first distance and the second distance. The exampleembodiment may also include, means for determining, based on thevertical distance of the object of interest above the radiationreceiver, a magnification of the object of interest in one of the firstradiograph or the second radiograph. The example embodiment may includemeans for scaling, based on the determined magnification, the image ofthe object of interest contained in one of the first radiograph and/orthe second radiograph in order to represent a physical size of theobject of interest. The example embodiment may include means forselecting, based on the scaled image of the object of interest, asurgical template closest in size to the physical size of the object ofinterest, where the surgical template is selected from a plurality ofsurgical templates of different sizes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a block diagram of a computing device; according toan example embodiment.

FIG. 2A represents a radiograph of a hip, according to an exampleembodiment.

FIG. 2B represents a template object overlaid on the radiograph of FIG.2A, according to an example embodiment.

FIG. 3 represents a digital templating user interface, according to anexample embodiment.

FIG. 4 represents a range of discrete template sizes, according to anexample embodiment.

FIG. 5A illustrates a radiation source positioned above a receiver,according to an example embodiment.

FIG. 5B illustrates a coordinate system attached to a receiver,according to an example embodiment.

FIGS. 6A and 6B illustrate the acquisition of radiographs from differentvertical radiation source positions, according to an example embodiment.

FIGS. 6C and 6D illustrate geometric models of FIGS. 6A and 6B,according to an example embodiment.

FIGS. 7A and 7B illustrate the acquisition of radiographs from differentvertical and horizontal radiation source positions and angularorientations, according to an example embodiment.

FIGS. 7C and 7D illustrate geometric models of FIGS. 7A and 7B,according to an example embodiment.

FIG. 7E illustrates a geometric model of FIG. 7B accounting for imageelongation, according to an example embodiment.

FIGS. 8A and 8B illustrate the acquisition of radiographs involving arotation of the radiation receiver, according to an example embodiment.

FIG. 9A illustrates an anteroposterior radiograph of a human hip,according to an example embodiment.

FIG. 9B illustrates a lateral radiograph of the human hip, according toan example embodiment.

FIG. 9C illustrates an axial view of the human hip, according to anexample embodiment.

FIG. 9D illustrates a geometric model of the rotated human hip,according to an example embodiment.

FIG. 10A illustrates an anteroposterior radiograph of a human hip in aneutral position, according to an example embodiment.

FIG. 10B illustrates an axial view of the human hip in the neutralposition of FIG. 10B, according to an example embodiment.

FIG. 10C illustrates an anteroposterior radiograph of the human hip in arotated position, according to an example embodiment.

FIG. 10D illustrates an axial view of the human hip in the rotatedposition of FIG. 10C, according to an example embodiment.

FIG. 11 illustrates a calibration marker being used to determine theposition of a radiation source, according to an example embodiment.

FIG. 12A illustrates another example of a calibration marker being usedto determine the position of a radiation source, according to an exampleembodiment.

FIG. 12B illustrates yet another example of a calibration marker beingused to determine the position of a radiation source, according to anexample embodiment.

FIG. 12C illustrates a geometric model of FIG. 12B, according to anexample embodiment.

FIGS. 13A and 13B illustrate a calibration marker being used todetermine a height of an object, according to an example embodiment.

FIGS. 14A and 14B illustrate a calibration marker attached to aradiation source, according to an example embodiment.

FIGS. 14C-14E illustrate an alternative approach of determining a heightof an object of interest, according to an example embodiment.

FIG. 15 illustrates an example user interface being used to identifyobjects of interest, according to an example embodiment.

FIGS. 16A and 16B illustrate a user interface being used to identifymultiple objects of interest, according to an example embodiment.

FIG. 17 illustrates a flow chart, according to an example embodiment.

FIG. 18 illustrates another flow chart, according to an exampleembodiment.

FIG. 19 illustrates yet another flow chart, according to an exampleembodiment.

DETAILED DESCRIPTION

Example methods, devices, and systems are described herein. It should beunderstood that the words “example” and “exemplary” are used herein tomean “serving as an example, instance, or illustration.” Any embodimentor feature described herein as being an “example” or “exemplary” is notnecessarily to be construed as preferred or advantageous over otherembodiments or features. Other embodiments can be utilized, and otherchanges can be made, without departing from the scope of the subjectmatter presented herein.

Thus, the example embodiments described herein are not meant to belimiting. Aspects of the present disclosure, as generally describedherein, and illustrated in the figures, can be arranged, substituted,combined, separated, and designed in a wide variety of differentconfigurations, all of which are contemplated herein.

Further, unless context suggests otherwise, the features illustrated ineach of the figures may be used in combination with one another. Thus,the figures should be generally viewed as component aspects of one ormore overall embodiments, with the understanding that not allillustrated features are necessary for each embodiment.

I. Overview

The embodiments described herein are generally directed at determiningthe magnification of an image of an object on a radiograph based on atleast two different radiographs. Example embodiments are also directedat determining the position and orientation of multiple objects based onat least two different radiographs. In an example embodiment, a firstradiograph of an object of interest may be obtained. A second radiographof the object of interest may be subsequently obtained from a differentposition, perspective, viewpoint, and/or orientation between a radiationsource and a radiation receiver than the first radiograph. Informationfrom the two radiographs may be used in combination in order todetermine a size (e.g., width, diameter), position, orientation, and/ormagnification of the object of interest. While the first and secondradiographs are two-dimensional (2D), the methods described herein mayenable the determination of three-dimensional (3D) information such asposition and orientation of an object of interest based on a combinationof the information contained in the two radiographs. The embodimentsdescribed herein may be used with templating techniques in order todetermine a template object closest in size to the object of interest.

For example, the embodiments herein may be used to accurately template areplacement prosthesis for a human hip joint using manual or digitaltemplating methods. A first radiograph of the hip may be obtained. Asecond radiograph of the hip may subsequently be obtained from adifferent position, perspective, viewpoint, and/or orientation between aradiation source and a radiation receiver than the first radiograph. Thetwo radiographs may be used in combination to determine the heights andlevels of magnification corresponding to different anatomical featuresof the hip. Portions of at least one of the two radiographs (wherein theportions are parts of images representing the different anatomicalfeatures) may be scaled according to the corresponding levels ofmagnification. The scaled portions may accurately represent the physicalsize and/or dimensions of the corresponding anatomical features.Additionally, based at least on the determined heights of the differentanatomical features, an orientation of at least portions of the hip maybe determined. For example, the rotation of the femur with respect tothe pelvis may be determined based on the heights of the femoral headand the femoral calcar. The scaled portions of the radiograph and thedetermined orientation of at least portions of the hip may be used incombination with digital templating to find a prosthesis that mostclosely matches the anatomical dimensions of the hip.

In the examples that follow, the different perspective of the secondradiograph relative to the first radiograph may be achieved by moving asource of radiation (e.g., an X-ray emitter) relative to a radiationreceiver (e.g. film, cassette, digital detector array) while keeping thereceiver stationary. Alternatively, the different perspective may beachieved by moving the receiver relative to the radiation source whilekeeping the source stationary. It may also be possible to move both thesource and receiver in combination, provided that the relative change inposition and orientation of the radiation source relative to thereceiver between the first radiograph and second radiograph is known,measured, determined, and/or accounted for in any relevant calculations.Moving the source and/or receiver may include horizontal translation,vertical translation, angular rotation, and/or any combination thereof.

II. Example Computing Device

The methods, operations, and/or example embodiments described herein maybe integrated into and/or performed by a computing device. The computingdevice may be, for example, a wireless computing device, tabletcomputer, desktop computer, laptop computer and/or a specializedcomputer integrated with a radiographic imaging device. For purposes ofexample, FIG. 1 is a simplified block diagram showing some of thecomponents of an example computing device 100 that may includeradiographic imaging components 124. However, computing device 100 doesnot require radiographic imaging components 124 in the embodimentsdescribed herein.

By way of example and without limitation, computing device 100 may be acellular mobile telephone (e.g., a smartphone), a computer (such as adesktop, notebook, tablet, handheld computer, or a specialized,purpose-built computer integrated with a radiographic imaging device), amedical device, a personal digital assistant (PDA), a home or businessautomation component, a digital television, or some other type of devicecapable of operating in accordance with the example embodimentsdescribed herein. It should be understood that computing device 100 mayrepresent a physical radiographic imaging device such as an X-rayimaging device, a particular physical hardware platform programmed tocarry out and/or provide instructions to a radiographic imaging deviceto carry out the operations described herein, or other combinations ofhardware and software that are configured to carry out the disclosedfunctions and operations.

As shown in FIG. 1, computing device 100 may include a communicationinterface 102, a user interface 104, a processor 106, data storage 108,and radiographic imaging components 124, all of which may becommunicatively linked together by a system bus, network, or otherconnection mechanism 110.

Communication interface 102 may allow computing device 100 tocommunicate, using analog or digital modulation, with other devices,access networks, and/or transport networks. Thus, communicationinterface 102 may facilitate circuit-switched and/or packet-switchedcommunication, such as plain old telephone service (POTS) communicationand/or Internet protocol (IP) or other packetized communication. Forinstance, communication interface 102 may include a chipset and antennaarranged for wireless communication with a radio access network or anaccess point. Also, communication interface 102 may take the form of orinclude a wireline interface, such as an Ethernet, Universal Serial Bus(USB), or High-Definition Multimedia Interface (HDMI) port.Communication interface 102 may also take the form of or include awireless interface, such as a Wifi, BLUETOOTH®, global positioningsystem (GPS), or wide-area wireless interface (e.g., WiMAX or 3GPPLong-Term Evolution (LTE)). However, other forms of physical layerinterfaces and other types of standard or proprietary communicationprotocols may be used over communication interface 102. Furthermore,communication interface 102 may comprise multiple physical communicationinterfaces (e.g., a Wifi interface, a BLUETOOTH® interface, and awide-area wireless interface).

User interface 104 may function to allow computing device 100 tointeract with a human or non-human user, such as to receive input from auser and to provide output to the user. Thus, user interface 104 mayinclude input components such as a keypad, keyboard, touch-sensitive orpresence-sensitive panel, computer mouse, trackball, joystick,microphone, and so on. User interface 104 may also include one or moreoutput components such as a display screen that, for example, may becombined with a presence-sensitive panel. The display screen may bebased on cathode ray tube (CRT), liquid-crystal display (LCD), and/orlight-emitting diode (LED) technologies, or other technologies now knownor later developed. User interface 104 may also be configured togenerate audible output(s), via a speaker, speaker jack, audio outputport, audio output device, earphones, and/or other similar devices.

In some embodiments, user interface 104 may include one or more buttons,switches, knobs, and/or dials that facilitate the configuration of aradiographic imaging device and the capturing or acquiring ofradiographs and/or representations of radiographs. It may be possiblethat some or all of these buttons, switches, knobs, and/or dials areimplemented by way of a presence-sensitive panel.

Processor 106 may comprise one or more general purpose processors—e.g.,microprocessors—and/or one or more special purpose processors—e.g.,digital signal processors (DSPs), graphics processing units (GPUs),floating point units (FPUs), network processors, or application-specificintegrated circuits (ASICs). In some instances, special purposeprocessors may be capable of image processing, image alignment, mergingimages, and feature detection (e.g. geometric feature such as a square,circle, or an approximation thereof) among other possibilities. Datastorage 108 may include one or more volatile and/or non-volatile storagecomponents, such as magnetic, optical, flash, or organic storage, andmay be integrated in whole or in part with processor 106. Data storage108 may include removable and/or non-removable components.

Processor 106 may be capable of executing program instructions 118(e.g., compiled or non-compiled program logic and/or machine code)stored in data storage 108 to carry out the various functions describedherein. Therefore, data storage 108 may include a non-transitorycomputer-readable medium, having stored thereon program instructionsthat, upon execution by computing device 100, cause the computing device100 to carry out any of the methods, processes, or operations disclosedin this specification and/or the accompanying drawings. The execution ofprogram instructions 118 by processor 106 may result in processor 106using data 112.

By way of example, program instructions 118 may include an operatingsystem 122 (e.g., an operating system kernel, device driver(s), and/orother modules) and one or more application programs 120 (e.g., camerafunctions, image processing functions, address book, email, webbrowsing, social networking, and/or gaming applications) installed oncomputing device 100. Similarly, data 112 may include operating systemdata 116 and application data 114. Operating system data 116 may beaccessible primarily to operating system 122, and application data 114may be accessible primarily to one or more of application programs 120.Application data 114 may be arranged in a file system that is visible toor hidden from a user of computing device 100.

Application programs 120 may communicate with operating system 122through one or more application programming interfaces (APIs). TheseAPIs may facilitate, for instance, application programs 120 readingand/or writing application data 114, transmitting or receivinginformation via communication interface 102, receiving and/or displayinginformation on user interface 104, and so on.

In some vernaculars, application programs 120 may be referred to as“apps” for short. Additionally, application programs 120 may bedownloadable to computing device 100 through one or more onlineapplication stores or application markets. However, application programscan also be installed on computing device 100 in other ways, such as viaa web browser or through a physical interface (e.g., a USB port) oncomputing device 100.

Radiographic imaging components 124 may include, but are not limited to,a radiation source, a radiation receiver, position feedback mechanismsconfigured to track the relative position between the radiation sourceand the radiation receiver, and/or any other components required for orintended to improve the function of a radiation imaging system orapparatus as described herein or otherwise known in the art. Radiationimaging components 124 may be controlled at least in part by softwareinstructions executed by processor 106. Radiation imaging components 124may also provide information to processor 106, user interface 104,communication interface 102, and/or data storage 108 indicating therelative spatial positioning of at least some of the radiographicimaging components 124.

It should be understood that the components of the computing device maybe distributed, logically or physically, over multiple devices of thesame or of a different type. Additionally, multiple computing devicesmay work in combination to perform the operations described herein. Forexample, a specialized computing device local to a radiographic imagingapparatus may be used to capture, store, and send at least oneradiograph or representation of a radiograph to a remote computingdevice. The remote computing device may process the radiographs orrepresentations of radiographs according to the example embodimentsdescribed herein. Other arrangements are possible.

III. Templating and Digital Templating

While many radiographic digital templating solutions are available andaim to provide accurate preoperative measurement of body parts, theyhave significant flaws. Specifically, existing solutions rely on aninaccurate and limited method of scaling radiographs and, as a result,only provide a gross estimation of the actual size of objects within aradiograph. Consequently, the existing solutions have limited to no usein reducing the cost of providing medical care and reducing surgicalcomplications.

Existing digital templating solutions (e.g., plain radiographictemplating solutions such as X-ray based templating) use one of twoknown methods of scaling radiographs. In one method, an object of knownsize, such as, for example, a coin, may be placed on a radiographicreceiver (cassette) at the time of imaging a body part of interest. Withall other factors kept constant, the magnification of the image of thebody part increases as the distance between the body part and theradiographic receiver increases. Accordingly, the image of the object ofknown size (e.g., the coin) is measured and the entire radiograph may bescaled according to the size of the image in relation to the actual,known size of the object. The scaling further assumes or estimates,based on the particular body part being measured, the average distancebetween the body part and the radiographic receiver based onstandardized anthropometric data of the average person from severaldecades ago.

However, this method has serious flaws in that it does not account foranthropometric and physiologic (e.g., obesity, muscularity, etc.)variations among humans. Consequently, the actual height of the objector objects of interest is not truly known. Accordingly, the determinedlevel of magnification of the object or objects of interest may beinaccurate since the actual height of the object or objects of interestis needed in order to determine the level of magnification.Additionally, this method incorrectly assumes that all objects withinthe radiograph are at the same distance from the radiographic receiver.As a result, this method does not accurately determine the magnificationof different objects within radiographs for each individual patient.This method only provides an estimate for the average sized person anddoes not account for the fact that anatomical features of the human bodyare at different distances to the radiation receiver when theradiographs are captured. Consequently, this method cannot be used toaccurately and reproducibly template bone features or bone lesions.

The second method relied upon by existing digital templating solutionsrequires the placement of an object of known size (e.g., a calibrationmarker) at the same height as the object of interest at the time ofcapturing the radiograph. By measuring the relative size between thecalibration marker and the image of the calibration marker contained inthe radiograph, the magnification of the image of the calibration markerin the radiographic image may be accurately determined. Accordingly,since the calibration marker is placed at the same height as the objectof interest, the magnification of the object of interest is equal to themagnification of the marker. Theoretically, this second method is moreaccurate than the first method. However, in practice, even this secondmethod faces significant limitations.

First, the second calibration marker method requires consistent andaccurate placement of the calibration marker at the same height as theobject of interest. The accuracy and consistency with which the markeris placed may vary between radiography technicians and medicalprofessionals having different levels of experience, education,understanding of the importance of and interest in the accurate andconsistent placement of the marker. As a result, significant human errormay result in inaccurate determination of the magnification of theobject of interest. Additionally, many large and obese patients may belarger than the radiation receiver used to capture the radiograph. As aresult, if, while acquiring a hip radiograph, the marker is placed inthe traditional position next to the greater trochanter of the femur,the marker may not appear in the image. The marker may need to be placedbetween the patient's legs, against the genitals, at approximately thesame height as the greater trochanter and acetabulum. The marker may notvisibly appear in the radiograph due to excess soft tissue obstructionsor placement beyond the radiographic receiver. Consequently, the markermay need to be repositioned and multiple images may need to be capturedto get the marker on a radiograph. This may lead to discomfort of thetechnician and the patient, and may result in inaccurate markerplacement as well as an increased risk of disease transmission.

Second, even if a medical professional with impeccable understanding andgrasp of the marker placement technique is used to place the marker, themedical professional still cannot accurately place the marker in allpatients. In order to accurately place the marker, the medicalprofessional must palpitate (feel) an anatomical feature or landmark(e.g. a bone feature) deep under the skin in order to determine theheight of the object of interest. However, in very muscular or obesepatients, the anatomical feature may not be palpable due to interposedsoft tissue. As a result, the marker may only be placed at anapproximate height of the object of interest.

Third, many deep anatomical features cannot be palpitated. In suchcases, marker placement is decided by referencing another anatomicalfeature that can be palpitated. However, once again, this methodrequires that the referenced anatomical feature be at the same height asthe object of interest and that the anatomical feature be palpable. Forexample, when templating hips for a total hip replacement, themagnification of the acetabulum may be determined. However, due to itslocation within the body, the acetabulum cannot be palpitated.Accordingly, the radiography technician or medical professional may havethe patient internally rotate the hip by 15 degrees to account forfemoral anteversion and place the greater trochanter of the femur, whichcan be palpitated, at approximately the same height as the acetabulum.

However, a technician may fail to internally rotate the hips by theprescribed amount. Additionally, many patients may not be able tointernally rotate their hips by 15 degrees due to arthritis, stiffness,or mechanical obstructions. Furthermore, recent studies indicate thatnot all hips are anteverted 15 degrees, and that there is actually largevariation in the degree of anteversion between individuals, oftenaffected by the sex and race of the patient. In one study, it has beenshown that up to 10% of African American males may have femoralretroversion. As a result, internally rotating the hips an average of 15degrees may not only be inaccurate for the general population, but mayactually worsen the accuracy of measurement in some individuals. As aresult, even if the technologist internally rotated the hip with eachpatient and the patient is able to physically perform this maneuver, themarker placement often may not be at the same height as the acetabulum.Therefore, the magnification for the acetabulum might not be accuratelydetermined. Worse, since this method is unable to measure femoralanteversion, the medical professional is unaware of any error in theprocess and will often use an incorrect measurement in planning andperforming surgery.

Finally, just like the first calibration marker method, this approachassumes that all objects represented by the radiograph are located atthe same height above the radiation receiver. The magnification ofobjects whose height is not equal to the height of the calibrationmarker is incorrect. Additionally, neither method provides anyinformation about the rotational position of the object of interest. Forexample, neither method provides any information about the degree ofrotation of the femur with respect to the pelvis. As a result,templating may be inaccurate, as the template used to size the femurcannot be rotated into the correct degree of rotation.

While more advanced methods such as magnetic resonance imaging (MM) andcomputer tomography (CT) have been used to determine the size ofanatomical features within a human body, these methods have severallimitations of their own. First, MM and CT scan devices may not bereadily accessible, particularly in rural locations. Second, Mill and CTscans are costly and may not be covered by insurance. Third, CT scansmay expose individuals to large doses of radiation, leading tomalignancy. Finally, MM and CT scans often require the individual to goto a different facility and are often not performed on the same day.

FIGS. 2A and 2B illustrate an example templating procedure.Specifically, FIG. 2A illustrates an anteroposterior (AP) radiograph 208of a human hip. The radiograph 208 shows acetabulum image 202, femoralhead image 204, and femoral calcar image 206. FIG. 2B illustrates atemplate object 200 overlaid atop the radiograph 208. The template 200may be selected from a plurality of available templates, as shown inFIG. 4. The plurality of templates may represent a range of availablesizes and shapes of replacement prostheses corresponding to the bodypart of interest (i.e. the body part shown on the radiograph beingtemplated). In the present example, the replacement prostheses may be ahip replacement prosthesis. Alternatively, the replacement prosthesesmay be intended to replace anatomical features of the knee, elbow,shoulder, or any other jointed or non-jointed portions of bone or softtissue.

An object of the templating process is to select a template object 200that most closely matches or resembles the anatomy of the particularbody part represented by radiograph 208. However, as previouslydiscussed, in some existing templating and digital templating solutions,the images of the different anatomical features (e.g. acetabulum image202, femoral head image 204, and femoral calcar image 206) contained inthe radiograph 208 may be magnified to different, unknown extents andmay be positioned in unknown or uncertain spatial orientations, leadingto errors and inaccuracies in the selection of template 200. In contrastto existing solutions, the example embodiments disclosed herein allowfor accurate determination of individual magnification levels where eachindividual magnification level is determined specifically for aparticular object of interest or anatomical feature contained within theradiograph 208.

The radiograph 208 used in the templating process may be a radiographicfilm, a photocopy of the radiographic film, or a digital representationof the radiograph stored in a non-transitory computer readable medium ofa computing device. Likewise, the template object 200, as well as theplurality of template objects from which template 200 is selected, maybe a clear plastic film having printed thereon a one-to-one scale imageof the template object. Templates representing different sizes ofprostheses may be placed over the radiograph 208 until a templateclosest in size to the anatomical features represented by radiograph 208is found. Alternatively, the template objects may be representeddigitally on a computing device. The digital representation of thetemplate may be overlaid on top of the digital representation ofradiograph 208 using a computing device. The overlay may be visuallydisplayed or illustrated on a display or user interface controlled bythe computing device. As will be later discussed, portions of theradiograph 208 or the template objects may be scaled to accuratelyrepresent the physical size of the anatomical features of interest.

FIG. 3 represents an example graphical user interface that may be usedwith a digital templating process. Specifically, FIG. 3 illustrates aportion of an AP hip radiograph with template objects 310 and 322overlaid thereon. The template objects 310 and 312 may represent aball-and-socket joint of a prosthesis intended to replace the proximalaspect of the femur and the acetabular socket of the pelvis. Thetemplate object 310, also called a shell template, may be used toevaluate the replacement of the acetabular socket. The template object312, also called a stem template, may be use to evaluate the replacementof the proximal aspect of the femur. The proximal aspect of the femurmay include at least the femoral head and femoral neck. The templateobject 312 may represent a stem portion 322 and a neck portion 320coupled to the ball portion of the stem template 312 at connection point318.

The user interface of FIG. 3 may enable a user to manipulate a pluralityof properties corresponding to template objects 310 and 312. Forexample, the user may specify a shell size of the template object 310.Likewise, the user may select a length of the neck portion 320, a sizeof the stem portion 322, as well as any other factors related to thesizing and positioning of the templates 310 and 312 over the radiograph.The plurality of properties corresponding to the template objects 310and 312 may be selected from and correspond to a plurality ofreplacement prostheses available for purchase from differentmanufacturers.

Heads up display 314 and a series of drop-down menus 316 may be used tomanipulate the properties of templates 310 and 312. For example,drop-down menus 316 may be used to select a prosthesis vendor, aparticular prosthesis model offered by the vendor, a size for the shellprosthesis template 310, a size for stem 322, and a length for neck 320,among others. Heads up display 314 may be used to, for example, select astem size and neck length of the template object 312. A computing devicemay execute program instructions causing the computing device toautomatically select a template object closest in size, shape, and/ororientation to the anatomical features contained in a radiograph.

FIG. 4 illustrates an example range of nine discrete template sizes 400corresponding to replacement prostheses. These templates may represent,for instance, the socket component of a ball-and-socket hip replacementprosthesis. Each of the nine discrete template sizes 400 is of adifferent size, and numbered from 1 to 9 in order of increasing size.Thus, template size 1 is smaller than template size 2, template size 2is smaller than template size 3, and so on. In some embodiments, more orfewer that nine template sizes may be available. Templates mayalternatively or additionally have different shapes in order to moreclosely match a given patient's anatomy. During the templating process,it may be possible to scale either the image of the particular object ofinterest (anatomical feature) contained in a radiograph or the templateobject based on the level of magnification determined to correspond tothe particular object. Alternatively, a custom template object may becreated and used in the templating process. A custom prosthesis may bemanufactured based on the custom template object.

As will be described in further detail to follow, the exampleembodiments described herein also enable a new feature of templatingplain radiographs. Namely, the embodiments described herein describe adetermination of a plurality of different heights corresponding todifferent objects of interest contained within a radiograph. Based onthe multiple heights, object rotation may be accurately determined and,as a result, a template may be rotated into an orientation that matchesthe rotation of the object or objects of interest. Thus, the embodimentsdescribed herein allow for selecting a template object substantiallymatching the shape of the object or objects of interest and improvingthe accuracy of measurement of the object of interest.

Alternatively, the example embodiments described herein may be usedwithout templating or digital templating processes. For example, theexample embodiments may be used in meniscal transplant surgery todetermine the size of a replacement allograft. Similarly, the exampleembodiments may be used to, for example, determine the actual physicalsize of a tumor or growth.

In another example, a bone, bone feature, bone fracture, and/or softtissue may be monitored or observed over time. For example, the objectof interest may be a bone fracture. The bone fracture may be monitoredover time in order to determine whether the fracture is healingproperly. Multiple radiographs of the bone fracture may be captured overtime, for example, every week, every two weeks, every month, or someother period of time. During each instance of capturing the radiographs,at least two images of the object of interest may be captured accordingto the example embodiments described herein in order to determine themagnification of the object of interest in at least one of theradiographs. The level of magnification in each of the multipleradiographs captured over time may be different due to, for example,variations in the positioning of the patient on the radiographicapparatus or due to changes in body composition of the patient.

When the level of magnification is not determined and accounted for inaccordance with the example embodiments described herein, theradiographs may be incorrectly interpreted. For example, immediatelyafter setting the fracture (placing and/or anchoring a broken(fractured) bone into the correct position for healing), an initialradiograph may be taken in order to ensure the bone is properly set(reduced) for healing. The image of the bone fracture may be magnifiedby a first level of magnification. Subsequently, for example, a weeklater, a follow-up radiograph may be captured of the bone fracture inorder to ensure that the bone fracture is properly healing. The image ofthe bone fracture may be magnified by a second level of magnification.The second level of magnification may be different due to, for example,patient positioning on the radiography apparatus. If the secondmagnification is different from the first magnification, the change inmagnification may create an appearance that the gap between the bones atthe fracture site has become larger, that bone overlap at the fracturesite has increased, or that the bone angular alignment has changed inthe follow-up radiograph compared to the initial radiograph. This mayincorrectly indicate or be interpreted as indicating that the fractureis not healing or is healing in an undesirable position. In fact, thefracture may be properly healing and may only appear to be changing dueto the level of magnification of the fracture in the follow-upradiograph being different from the level of magnification of thefracture in the initial radiograph.

In contrast, when the initial and follow-up radiographs are acquired andprocessed according to the example embodiments described herein, thisproblem may be reduced or eliminated. Determining the level ofmagnification corresponding to each object of interest in eachradiograph may allow the images of the object of interest contained inthese radiographs to be scaled to accurately represent the actualphysical size of the objects of interest. For example, two initialradiographs of the bone fracture may be taken in order to determine themagnification of the image of the bone fracture in at least one of thetwo initial radiographs, according to the example embodiments describedherein. The image of the bone fracture contained in at least one of thetwo initial radiographs may be scaled according to the determinedmagnification in order to accurately represent the actual physical sizeof the bone fracture. This process may be repeated for the follow-upradiograph. The initial and follow-up radiograph may be accuratelycompared in order to determine whether the bone fracture is properlyhealing. Accordingly, the effect of any variations in magnificationacross the multiple radiographs taken over time may be reduced oreliminated.

Furthermore, the example embodiments described herein may be performedbefore, during, and/or after surgery. Additionally, the embodiments arenot limited to use with humans and may be used, for example, inveterinary medical procedures. Yet further, the example embodimentsdescribed herein may be used outside of the medical field in order toaccurately determine the respective sizes of objects of interest, asdescribed herein.

IV. Radiographic Devices

FIG. 5A depicts an example arrangement of a radiation source 500positioned above a radiation receiver 504. The object of interest 502 isshown positioned between the radiation source 500 and receiver 504. Aradiograph 510 of the object of interest is shown in the top view 508 ofreceiver 504. The object 502 may be a part of a human body, such as thehead of a femur or the head of a humerus. In general, the object 502 maybe any physical structure not limited to bones or parts of the humanbody. The receiver 504 may be any type of film, material, or devicethat, when exposed to radiation 506 from source 500, results in thecreation of an image 510 of object 502. The receiver 504 may also bereferred to as a cassette or detector.

The diameter of image 510 is larger than the diameter of object 502. Inother words, the image 510 is a magnified (enlarged) representation ofthe object 502. The embodiments described herein are directed atdetermining the level of magnification of the image 510 of object 502 sothat the image 510 can be used to accurately represent the actualphysical size of object 502.

FIG. 5B illustrates an example coordinate system 512 attached toreceiver 504. The coordinate system 512 is a Cartesian coordinate systemcomprising an x-axis corresponding to a width of image 510, a y-axiscorresponding to a length of image 510, and a z-axis corresponding to aheight of objects (e.g., object 502) above the receiver 504. Someembodiments may alternatively utilize a polar coordinate system, acylindrical coordinate system, a spherical coordinate system, or anycombination thereof. Other choices of coordinate systems are possible.Some embodiments may chose a coordinate system that simplifies thecomputation required to determine the magnification of image 510.

In general, the embodiments described herein involve knowing, measuring,and/or determining the relative position between the radiation source500 and the receiver 504, the object 502 and the receiver 504, theradiation source 500 and the object 502, and/or the image 510 and thereceiver 504. Radiographic imaging systems may be automated such thatthe relative position between the source 500 and receiver 504 may beknown based on position feedback mechanisms. For example, theradiographic system may be programmed, based on the body part ofinterest, to automatically move into a particular position, acquire afirst image, move to a second position, and acquire a second image, andso on. Moving to a particular position may comprise movement of theradiation source 500, the receiver 504, or a combination of both.Alternatively or additionally, a holder or housing containing theradiation receiver 504 may be moved. For example, the holder or housingmay be a radiography table on which a patient or a body part of thepatient is disposed. Moving to the particular position may involvemoving the radiography table along with the patient or body part of thepatient without changing the relative position between the patient orthe body part of the patient and the radiography table. Other variationsmay be possible.

The radiographic imaging system may associate corresponding spatialposition data with each radiograph. For example, when the radiograph iscaptured, stored as a digital file, and/or represented on a display of acomputing device, the spatial position data (based on an output of theposition feedback mechanism) may be stored and/or represented asmetadata associated with the digital file. The metadata may be a part ofthe digital radiograph image file or may be another file linked to thedigital radiograph image file. Alternatively, the metadata may beincluded directly on a physical radiograph. The metadata may be printedin the corner of the radiograph such that it does not obstruct any ofthe images of anatomical features contained in the radiograph. Themetadata may be retrieved automatically from a radiographic device by acomputing device or may be provided to the computing device by atechnician.

The spatial position data contained in the metadata may comprise 3Dspatial position coordinates (e.g., (x,y,z) Cartesian coordinates,(θ,ϕ,r) polar coordinates) and angular orientation information of theradiation source 500 and the receiver 504. The spatial position data mayinclude coordinates of the radiation source 500 in relation to (in aframe of reference attached to) the radiation receiver 504. Alternativeembodiments may represent the spatial position data as coordinates ofthe radiation receiver 504 in relation to the radiation source 500. Someembodiments may alternatively represent the spatial position data ascoordinates of the radiation source 500 and the radiation receiver 504relative to an absolute reference frame. The radiograph and theassociated spatial position data may subsequently be utilized by theembodiments described herein to determine the magnification, position,and spatial orientation of the object of interest.

In radiographic systems without automated position feedback,determination of the relative spatial position between the radiationsource 500 and the receiver 504 may rely on a radiography technician.The radiographic system may include a light source projecting areference light point onto a ruler located on a radiographic tablehousing the radiation receiver. The position of the radiation source 500in relation to receiver 504 may be manually determined and recorded bythe radiography technician. For example, using the reference light andthe ruler, the radiation source 500 may first be centered above receiver504, the relative vertical, horizontal, and angular positions may berecorded, and the first radiograph may be captured. The technician maysubsequently change the angle of the radiation source 500 (using aninclinometer present and/or attached to the radiographic system) to adesired angle. The radiation source 500 may then be translatedhorizontally and vertically such that the reference light is againcentered on the receiver 504. The technician may record the relativevertical, horizontal, and angular positions and may subsequently capturethe second radiograph. Other procedures, both automated and manual, maybe possible provided that the relative spatial position and orientationof the radiation source 500 and receiver 504 are known or may bemeasured or determined and provided that the spatial position andorientation information may be associated with the corresponding image.

V. Determining Object Height and Magnification

FIGS. 6A and 6B illustrate an example embodiment wherein the first image610 and the second image 612 are captured at different distances betweenthe radiation source 600 and the receiver 604. These and other figuresare shown adjacent to each other to more clearly illustrate aspects ofthe embodiments. A vertical line is shown in these and other figures toclearly separate elements of the adjacent figures. In FIGS. 6A and 6B,the source 600 is assumed to be centered above the object 602.Additionally, the height (vertical distance) h of the object 602 abovethe receiver 604 as well as the diameter of the object a are assumed tobe unchanged between when the two images are captured. Furthermore,object 602 is shown as a 2D cross-section of a sphere. However,alternative embodiments may model object 602 as different shapes (e.g.,disk or cylinder) and may perform the corresponding calculations basedon the particular shape of object 602.

In FIG. 6A, the radiation source 600 is located a distance d₁ above thereceiver 604 at position 614. The radiation source 600 emits radiation606 which creates an image 610, as illustrated in the top view 608A ofreceiver 604. The top view 608A may also represent the radiographproduced when object 602 is exposed to radiation 606 from radiationsource 600 when radiation source 600 is at position 614. The image 610has a measurable diameter e₁. After acquisition of image 610, theradiation source 600 may be moved from position 614 to position 616 asshown in FIG. 6B.

In FIG. 6B, the radiation source 600 is located a distance d₂ above thereceiver 604 at position 616. The radiation source 600 emits radiation606 which creates an image 612, as illustrated in the top view 608B ofreceiver 604. The top view 608B may also represent the radiographproduced when object 602 is exposed to radiation 606 from radiationsource 600 when radiation source 600 is at position 616. The image 612has a measurable diameter e₂. The image 612, produced when the radiationsource is at position 616, has a greater degree of magnification thanthe image 610, produced when the source is at position 614. This is dueto the position 616 being closer to receiver 604 than position 614.Accordingly, the diameter e₂ of image 612 is greater than the diametere₁ of image 610. The order in which the images 610 and 612 are acquiredis not important. For example, image 610 may be acquired after acquiringimage 612 by moving the radiation source from position 616 to position614. Similarly, the distances d₁ and d₂ can be varied provided that theyare not equal.

It can be observed from FIGS. 6A and 6B that, due to magnification, thediameters of the images 610 and 612 (e₁ and e₂ respectively) are greaterthan the diameter a of the object of interest 602. The images 610 and612 may be scaled by the corresponding level of magnification in orderto accurately represent the actual physical size (diameter) a of object602. The magnification M₁ of image 610 may be expressed by the ratio ofthe size of image e₁ to the actual physical size of the object a as inEquation (1). The magnification M₂ of image 612 can likewise be computedas Equation (2).

M ₁ =e ₁ /a  (1)

M ₂ =e ₂ /a  (2)

While e₁ and e₂ can be measured directly from the correspondingradiographs, the diameter a may be computed using trigonometricproperties. Similarly, d₁ and d₂ may be obtained directly from theradiation source hardware or software. For example, a radiography systemmay utilize a position feedback mechanism to monitor the relativeposition between the radiation source 600 and receiver 604.Alternatively, the distances may be measured manually, using physicalmeasuring devices, and may subsequently be provided to the software orhardware executing the embodiments described herein.

In general, the images 610 and 612 may be contained on two differentradiographs or on a single radiograph acquired using a double exposure.For example, image 610 may be captured on a first radiographic film.Image 612 may subsequently be captured on a second radiographic film.Alternatively, both images 610 and 612 may be captured on the same film,potentially resulting in some overlap between the images 610 and 612.Similarly, representations of the images 610 and 612 and/orrepresentations of the respective radiographs containing the images 610and 612 may be displayed separately or as image overlays. For example, arepresentation of the radiograph containing image 610 may be overlaid ontop of a display of a representation of the radiograph containing image612.

FIG. 6C shows an example way of modeling the geometry of the radiationsource 600 located at position 614, the object 602, and the receiver604. Specifically, based on triangles 618 and 620, the tangent of theangle θ₁ may be expressed as Equations (3) and (4) respectively.

$\begin{matrix}{{\tan \left( \theta_{1} \right)} = \frac{a/2}{d_{1} - h}} & (3) \\{{\tan \left( \theta_{1} \right)} = \frac{e_{1}/2}{d_{1}}} & (4)\end{matrix}$

Equations (3) and (4) may be combined into Equation (5) to solve for a.

$\begin{matrix}{{\frac{a/2}{d_{1} - h} = \frac{e_{1}/2}{d_{1}}}{a = \frac{e_{1}\left( {d_{1} - h} \right)}{d_{1}}}} & (5)\end{matrix}$

Plugging Equation (5) back into Equation (1) yields Equation (6).

$\begin{matrix}{M_{1} = \frac{d_{1}}{d_{1} - h}} & (6)\end{matrix}$

An equivalent procedure may be carried out for the image 612 acquiredwith the radiation source at position 616. The size (diameter) a ofobject 602 may be expressed by Equation (7) and the magnification M₂ ofthe image 612 may be expressed by Equation (8).

$\begin{matrix}{a = \frac{e_{2}\left( {d_{2} - h} \right)}{d_{2}}} & (7) \\{M_{2} = \frac{d_{2}}{d_{2} - h}} & (8)\end{matrix}$

In order to determine the magnification of either image 610 or 612,example embodiments may determine the height h of the object 602 bycombining Equations (5) and (7), resulting in Equation (9).

$\begin{matrix}{{\frac{e_{1}\left( {d_{1} - h} \right)}{d_{1}} = \frac{e_{2}\left( {d_{2} - h} \right)}{d_{2}}}{{e_{1}{d_{2}\left( {d_{1} - h} \right)}} = {e_{2}{d_{1}\left( {d_{2} - h} \right)}}}{h = \frac{d_{1}{d_{2}\left( {e_{2} - e_{1}} \right)}}{{d_{1}e_{2}} - {d_{2}e_{1}}}}} & (9)\end{matrix}$

It may be apparent from Equation (9) that at least two images are neededin order to determine the height h of object 602. Additionally, in thisparticular embodiment, the images must be taken from two differentheights. Namely, the distances d₁ and d₂ cannot be equal in order toobtain a non-trivial solution for h. The height h may now be used withEquations (6) and (8) to determine the magnifications M₁ and M₂. Eitheror both of images 610 and 612 may be scaled according to thecorresponding level of magnification (M₁ and M₂ respectively) todetermine and display the actual size a of the object of interest 602.

The determined actual size may be used to select a template closest inshape and size to the object of interest. For example, the object ofinterest may be a femur or the corresponding acetabulum (femoralsocket). The templates may represent a plurality of availablereplacement femoral stem prosthesis and/or corresponding acetabularprostheses. Selecting a replacement prosthesis closest in size and shapeto the actual anatomical size of a patient's femur and acetabulum priorto a hip replacement surgery may ensure that the replacement prosthesiswill properly fit the patient's anatomy.

A computing device may be programmed or configured to carry out theoperations and/or the embodiments described herein. For example, thecomputing device may obtain two radiographs or digital representationsof the two radiographs (e.g., image files of the radiographs). A firstradiograph may contain image 610. The first radiograph may be associatedwith first metadata indicating the distance d₁. Alternatively, the firstmetadata may contain the spatial coordinates of the radiation source 600and radiation receiver 604. The distance d₁ may be determined from thespatial coordinates using arithmetic operations. Similarly, a secondradiograph may contain image 612. Likewise, the second radiograph may beassociated with a second metadata indicating, either directly orindirectly, the distance d₂.

The computing device may subsequently scan or search the firstradiograph or digital representation thereof to locate the image 610.Similarly, the second radiograph or digital representation thereof maybe scanned or searched to locate the image 612. For example, thecomputing device may be programmed to search for geometric shapes orfeatures such as circles in order to identify the images 610 and 612.Alternatively, a user may identify the images 610 and 612 using agraphical user interface that the computing device is programmed orconfigured to implement. After locating images 610 and 612 in therespective radiographs, the diameters e₁ and e₂ of images 610 and 612,respectively, may be determined by, for example, counting the number ofpixels along a line that defines the diameter of each circular image 610and 612.

The computing device may use the determined values of d₁, d₂, e₁, and e₂to implement Equations (1) to (9), as detailed above, in order todetermine the magnifications M₁ and M₂ of images 610 and 612,respectively. The diameters e₁ and e₂ of images 610 and 612 may bemodified according to the corresponding levels of magnification M₁ andM₂ to represent the actual physical size of object 602. The modificationmay comprise temporarily adjusting the visual display of the digitalrepresentations of images 610 and 612. Alternatively, the modificationmay comprise permanently storing the adjusted size of images 610 and 612in a file containing the respective images and/or the correspondingmetadata. Other variations are possible. The computing device may alsobe programmed or configured to perform or interface with a deviceconfigured to perform templating and/or digital templating as describedwith respect to FIGS. 2-4.

FIG. 6D illustrates an alternative way of modeling the geometry of theradiation source 600 located at position 614, the object 602, and thereceiver 604. This alternative embodiment more accurately accounts forthe spherical shape of the object of interest 602. The size (diameter) aof object 602 is exaggerated in FIG. 6D in order to more clearly pointout the geometric basis for the following calculations. Specifically, atangent to a circle is always perpendicular to the radius of the circle.Consequently, triangle 622 more accurately models the geometry of thisparticular embodiment (where object 602 is spherical) than triangle 618.Based on triangle 622, the sine of the angle θ₁ may be expressed as inEquation (10).

$\begin{matrix}{{\sin \left( \theta_{1} \right)} = \frac{a/2}{d_{1} - h}} & (10)\end{matrix}$

Likewise, Equation (11) may be written based on triangle 624.

$\begin{matrix}{{\tan \left( \theta_{1} \right)} = \frac{e_{1}/2}{d_{1}}} & (11)\end{matrix}$

However, the calculations presented with respect to FIG. 6C are accuratefor spherical object 602 when the angle θ₁ is small sincesin(θ₁)≈tan(θ₁) for small θ₁.

Example embodiments may utilize either the geometric model of FIG. 6C or6D provided that the assumptions behind the utilized model are takeninto consideration. For example, Equation (3), based on the model ofFIG. 6C, is accurate when θ₁ is small enough such that sin(θ₁)≈tan(θ₁).Under such conditions, both Equations (3) and (10) may produce accurateresults that can reliably be used in subsequent calculations. When theassumption of small θ₁ is no longer true, then Equation (10) may be usedbecause using Equation (3) may lead to inaccurate calculation results.Accordingly, either model may be used provided that the assumptions ofthe model hold true under the specific use conditions.

The distances e₁ and d₁, illustrated in FIG. 6D, are known or may bemeasured directly. Consequently, the angle θ₁ can be expressed byEquation (12).

$\begin{matrix}{\theta_{1} = {\tan^{- 1}\left( \frac{e_{1}/2}{d_{1}} \right)}} & (12)\end{matrix}$

A second image may be taken at a distance d₂, producing an image withdiameter e₂ in a manner similar to that described with respect to FIGS.6A and 6B. The angle θ₂ may be analogously modeled according toEquations (13), (14), and (15).

$\begin{matrix}{{\sin \left( \theta_{2} \right)} = \frac{a/2}{d_{2} - h}} & (13) \\{{\tan \left( \theta_{2} \right)} = \frac{e_{2}/2}{d_{2}}} & (14) \\{\theta_{2} = {\tan^{- 1}\left( \frac{e_{2}/2}{d_{2}} \right)}} & (15)\end{matrix}$

Based on the first image, the size a of object 602 may be expressed byEquation (16), derived from Equation (10).

a=2(sin(θ₁))(d ₁ −h)  (16)

Based on the second image, the size a of the object 602 may be expressedby Equation (17), derived from Equation (13).

a=2(sin(θ₂))(d ₂ −h)  (17)

Equations (16) and (17) may be combined and solved for h as shown byEquation (18), where θ₁ and θ₂ are given by Equations (12) and (15),respectively.

$\begin{matrix}{{{2\left( {\sin \left( \theta_{1} \right)} \right)\left( {d_{1} - h} \right)} = {2\left( {\sin \left( \theta_{2} \right)} \right)\left( {d_{2} - h} \right)}}{h = \frac{{d_{2}{\sin \left( \theta_{2} \right)}} - {d_{1}{\sin \left( \theta_{1} \right)}}}{{\sin \left( \theta_{2} \right)} - {\sin \left( \theta_{1} \right)}}}} & (18)\end{matrix}$

The height expressed by Equation (18) may now be used to compute thelevels of magnification expressed by Equations (6) and (8). The computedmagnifications M₁ and M₂ may be used to appropriately scale at least oneof the corresponding image 610 and 612, as described with respect toFIGS. 6A and 6B. The scaled image may be used to determine a template(representing a replacement part for the object of interest 602) closestin shape and size to the object of interest 602.

As with FIG. 6C, a computing device may be programmed or configured toimplement the operations described with respect to FIG. 6D. For example,the computing device may obtain, acquire, or capture two radiographs ordigital representations thereof. A first radiograph may contain image610 and be associated with metadata indicating or used to determine thedistance d₁. Likewise, a second radiograph may contain image 612 and beassociated with metadata indicating or used to determine the distanced₂. The computing device may be programmed to determine the distances e₁and e₂ using image recognition and/or feature detection algorithms. Thecomputing device may also be programmed to implement Equations (6), (8),and (10) to (18), as detailed above, in order to determine themagnifications M₁ and M₂ or images 610 and 612, respectively. The images610 and 612 may be scaled according to magnifications M₁ and M₂ and maybe used in templating and/or digital templating, as described withrespect to FIGS. 2-4.

In general, although the distances e₁ and e₂ used to determine thecorresponding level of magnification may be, in some embodiments,diameters of the object of interest, the distances e₁ and e₂ mayalternatively be measured in a different manner. For example, thedistances e₁ and e₂ may be distances of a particular object of interestor feature thereof measured in relation to a reference point (anchorpoint) in a radiograph, as described in detail with respect to theembodiments depicted in FIGS. 14C-14E.

FIGS. 7A and 7B illustrate an alternative embodiment wherein the secondimage 712 is captured while the vertical and horizontal positions of theradiation source 700 are different from the vertical and horizontalpositions of the radiation source 700 used to capture the first image710. FIG. 7B additionally shows the radiation source 700 rotatedrelative to its original position in FIG. 7A. The radiation source 700may be rotated in order to ensure that the emitted radiation 706, or atleast a portion thereof, is aimed at the object of interest 702.However, the radiation source 700 may also be rotated in order to take asecond image 712 from a different perspective than image 710. While FIG.7B shows the radiation source 700 in a rotated position relative to theposition illustrated in FIG. 7A, alternative embodiments may bepracticed without rotating the radiation source 700.

In general, although FIG. 7B illustrates the radiation source 700translated vertically, translated horizontally, and rotated relative tothe position 714 in FIG. 7A, alternative embodiments may function byperforming only one of the described movements. For example, someembodiments may involve only horizontal translation of the radiationsource 700 or both horizontal translation and rotation of the radiationsource 700. In alternative embodiments, the radiation receiver 704 maybe moved while the radiation source 700 is held in a fixed position. Theembodiment illustrated by FIGS. 7A and 7B includes all three movementtypes (horizontal translation, vertical translation, and rotation) forthe purpose of providing a generalized example geometric model.

Furthermore, although the example diagrams are two-dimensional, theembodiments described herein are equally applicable to three dimensions.For example, a different perspective of the object of interest may beachieved via horizontal translation in the x-direction, horizontaltranslation in the y-direction, vertical translation in the z-direction,rotation along the pitch-axis, rotation along the roll-axis, or anycombination thereof, provided that the geometry of the changedperspective is properly accounted for, as demonstrated herein.

FIG. 7A illustrates radiation source 700 located a distance d₁ above thereceiver 704. The radiation source 700 emits radiation 706, whichcreates an image 710, as illustrated in the top view 708A of receiver704. The top view 708A may also represent the radiograph produced whenobject 702 is exposed to radiation 706 from radiation source 700 whenradiation source 700 is at position 714. The image 710 has a diametere₁. Line 720 illustrates the x-position of the radiation source 700above receiver 704. After acquisition of image 710, the radiation source700 may be moved from position 714 to position 716 as shown in FIG. 7B.In FIG. 7B, the radiation source 700 is located a distance d₂ above thereceiver 704 at position 716. Additionally, the radiation source 700 hasbeen translated horizontally to the left as indicated by arrow 718. Thedifference in x-position of line 720 and line 722 illustrates the extentof horizontal translation.

In FIG. 7B, radiation source 700 emits radiation 706 which creates animage 712, as illustrated in the top view 708B of receiver 704. The topview 708B may also represent the radiograph produced when object 702 isexposed to radiation 706 from radiation source 700 when radiation source700 is at position 716. The image 712 has a diameter e₂. The image 712produced by the radiation source at position 716 has a greater degree ofmagnification than the image 710 produced when the source is at position714. This is due to position 716 being vertically closer to receiver 704than position 714. Accordingly, the diameter e₂ of image 712 is greaterthan the diameter e₁ of image 710. Additionally, as the source istranslated to the left from position 714 to position 716, the projectedimage 712 translates to the right of the position of projected image710.

As with the embodiment of FIGS. 6A and 6B, the order in which the images710 and 712 are acquired is not important. For example, image 710 may beacquired after acquiring image 712 by moving the radiation source fromposition 716 to position 714. Similarly, the distances d₁ and d₂ may bevaried provided that they are known (through automated methods orexplicit measurements) and enable the acquisition of images ofsufficient quality for analysis. The distances d₁ and d₂ may be equal insome embodiments.

In some embodiments, the resulting images of the object of interest maybe elongated due to the geometric relationship of the radiation source,the object of interest, and the receiver. For example, the exampleembodiment illustrated by FIG. 7B may result in the spherical object 702producing an elliptical image (not depicted) as opposed to the circularimage 712. Specifically, the extent of image elongation will depend onthe degree of rotation of the radiation source 700, the difference inhorizontal (lateral) position between the object of interest 702 and theradiation source 700, and the size (diameter) a of the object 702. Forexample, the embodiment illustrated in FIGS. 6A and 6B produces noelongation because the object of interest 602 is positioned directlybeneath the radiation source 600.

The example embodiments described herein may be operated in a mannerthat does not result in a significant degree of image elongation. Forexample, in FIG. 7B, the difference in x-position between lines 720 and722, corresponding to the horizontal translation of radiation source 700from position 714 to position 716, may be kept small such that theextent of image elongation may be ignored without compromising themathematical accuracy of subsequent computations. Alternativeembodiments may remove, adjust, and/or account for any elongationpresent in the images using software algorithms or specialized hardwareperforming similar functions. Removal or adjustment of elongation may bebased on any known or calculated quantities pertaining to the geometricrelationship between the radiation source, the object of interest, andthe receiver. In some embodiments, elongation may be removed regardlessof the extent of elongation present in the image. Alternativeembodiments may remove or account for elongation only when it isdetermined that the extent of elongation present in a particular imageis above a threshold value. Example methods of accounting for imageelongation are illustrated in and described in detail with respect toFIG. 7E.

Similar to FIGS. 6A and 6B, it can be observed from FIGS. 7A and 7B thatdue to magnification, the sizes (diameters) of the images 710 and 712(e₁ and e₂ respectively) are greater than the size (diameter) a of theobject of interest 702. In order to accurately represent the actualphysical size (diameter) a of object 702, the images 710 and 712 may bescaled by the corresponding level of magnification. When the extent ofimage elongation is small (alternatively, when image elongation isremoved altogether using software algorithms), the magnification M₁ ofimage 710 may be expressed according to Equations (1) and (6). Likewise,the magnification M₂ of image 712 can be expressed according toEquations (2) and (8).

FIG. 7C shows an example way of modeling the geometry of the embodimentillustrated in FIGS. 7A and 7B. The size (diameter) a of object 702 isexaggerated to more clearly illustrate the relevant geometry. As withthe embodiment illustrated in FIGS. 6A and 6B, the present embodimentdetermines the level of magnification of images 710 and 712 to scale atleast one of the images by the corresponding level of magnification inorder to determine the actual size (diameter) a of object 702.

The length x₂ is the horizontal distance (difference in the x-coordinateof position) between the radiation source 700 at position 716 and thecenter of the corresponding image (the image 712 taken from position716). The length x₁ represents an analogous relationship between theradiation source 700 at position 714 and the corresponding image 710.The horizontal positions 720 and 722 corresponding to radiation source700 locations 714 and 716, respectively, may be determined from positionfeedback mechanisms of the radiography system or may alternatively bedetermined by a radiography technician. The centers of images 710 and712 may be determined manually, based on user input, or automatically insoftware using image processing algorithms. For example, when images 710and 712 are or are expected to be circles or approximately circular, thecenters may be found using, for example, the Hough Circle Transform. Thecenters of images 710 and 712 may also be determined by any of themethods described later with respect to FIG. 7E. The distances x₁ and x₂may be determined manually, via user input, or automatically, by acomputing device executing specialized software, based on the parametersdescribed above.

In embodiments that acquire images with minimal or no elongation, thex-coordinate of the image corresponding to the center of the object ofinterest may be the center of the produced image. For example, in thepresent embodiment, the object 702 is spherical and produces circularimages 710 and 712. The x-coordinates of images 710 and 712corresponding to the center of object 702 are the x-coordinates of themidpoints (centers) of the respective images. Objects of interest mayhave different shapes and may be modeled according to the methodsdescribed herein by accounting for the geometric shape of the object ofinterest in the relevant calculations. Alternative embodiments mayacquire images having a non-negligible amount of elongation. The pointin the image corresponding to the center of the object of interest maybe determined by accounting for the amount of image elongation asillustrated in and described in detail below with respect to FIG. 7E.

In the case of a fully automated radiography system, the position (x, y,and z) of the radiation source 700 can be determined in relation toreceiver 704 and images 710 and/or 712 based on position feedbackassociated with radiation source 700 and receiver 704. Alternativeembodiments may function with a system without automated positionfeedback. Specifically, a technician operating the radiation source 700may keep track of the position of radiation source 700 and maysubsequently input the information into hardware or software toassociate the coordinates of the radiation source 700 at position 716with image 712. Example embodiments may determine the position of thecenter of the image 712 using software or specialized hardware.Alternatively, the position of the center of image 712 may be determinedmanually by a technician. The determined position may subsequently beentered into computing software or hardware. Automation of the methodsdescribed herein may result in more accurate measurements andcomputation.

Based on triangle 724 of FIG. 7C, the tangent of the angle B may beexpressed by Equation (19), where the distance d₂ is the height ofradiation source 700 above receiver 704 at position 716.

$\begin{matrix}{{\tan (B)} = \frac{d_{2}}{x_{2}}} & (19)\end{matrix}$

Accordingly, angle B may be determined according to Equation (20).

$\begin{matrix}{B = {\tan^{- 1}\left( \frac{d_{2}}{x_{2}} \right)}} & (20)\end{matrix}$

Similarly, based on triangle 724, the angle α₂ may be computed accordingto Equation (21).

α₂=90°−B  (21)

Based on triangle 728 of FIG. 7C, the tangent of angle A may be computedaccording to Equation (22) where the distance d₁ is the height ofradiation source 700 above receiver 704 at position 714.

$\begin{matrix}{{\tan (A)} = \frac{d_{1}}{x_{1}}} & (22)\end{matrix}$

Accordingly, angle A may be determined according to Equation (23).

$\begin{matrix}{A = {\tan^{- 1}\left( \frac{d_{1}}{x_{1}} \right)}} & (23)\end{matrix}$

Similarly, based on triangle 728, the angle α₁ may be computed accordingto Equation (24).

α₁=90°−A  (24)

Based on triangle 726, of FIG. 7C, the height h of the object ofinterest 702 may be expressed according to Equation (25).

h=(y)sin(B)  (25)

Likewise, based on triangle 730, the height of h of the object ofinterest 702 may be expressed according to Equation (26).

h=(z)sin(A)  (26)

Based on triangle 732 shown in FIG. 7D, hypotenuse y of triangle 726 andhypotenuse z of triangle 730 may be determined using the law of sinesaccording to Equation (27), where n is the distance between the centerof image 710 and image 712.

$\begin{matrix}{\frac{\sin (A)}{y} = {\frac{\sin (B)}{z} = \frac{\sin (C)}{n}}} & (27)\end{matrix}$

The distance n is a measurable quantity that may be determined directlyfrom the radiographs using software and/or hardware image processingmethods. Alternatively, n may be determined using the methods describedwith respect to FIG. 7E.

Based on FIG. 7C, the angle C may be determined according to Equation(28).

C=α ₁+α₂  (28)

Accordingly, by combining Equations (20) or (28) with Equation (27),hypotenuse y may be expressed according to Equation (29).

$\begin{matrix}{y = \frac{(n){\sin (A)}}{\sin (C)}} & (29)\end{matrix}$

Analogously, by combining Equations (23) or (28) with Equation (27),hypotenuse z may be expressed according to Equation (30).

$\begin{matrix}{z = \frac{(n){\sin (B)}}{\sin (C)}} & (30)\end{matrix}$

Finally, by combining Equations (25) and (29) or Equations (26) and(30), the height h of the object of interest 702 may be determinedaccording to Equation (31).

$\begin{matrix}{h = \frac{(n){\sin (A)}{\sin (B)}}{\sin (C)}} & (31)\end{matrix}$

With the height h known, the magnification can be computed for image 710and/or image 712 according to Equations (6) and (8), respectively. Theimages may be scaled according to the corresponding level ofmagnification in order to determine and display the actual physical size(diameter) a of the object of interest 702.

As previously mentioned, alternative embodiments may determine themagnification of the object of interest 702 by considering the extent ofimage elongation. FIG. 7E illustrates another example geometric model ofthe embodiment described with respect to FIGS. 7A and 7B. Themagnification M₂ of the image 712 produced when the radiation source 700is at position 716 can be expressed according to Equation (32). The sizel₂+r₂ of the image 712, labeled as e₂ in FIG. 7B, may be determineddirectly from the radiograph containing image 712. Based on triangle736, the size a of the object 702 may be expressed according to Equation(33).

$\begin{matrix}{M_{2} = \frac{l_{2} + r_{2}}{a}} & (32) \\{a = {2f\; {\sin \left( \theta_{2} \right)}}} & (33)\end{matrix}$

The distance l₂, corresponding to the left image portion of image 712,and the distance r₂, corresponding to the right image portion of image712, may be determined explicitly in order to accurately locate thepoint in the image 712 corresponding to the center of object 702.Specifically, based on triangle 734, the angle β₂ may be derived fromEquation (34) and expressed according to Equation (35), where z₂ is aknown, measurable quantity corresponding to the distance between thex-coordinate of position 716 (represented by line 722) and the left edgeof image 712.

$\begin{matrix}{{\tan \left( \beta_{2} \right)} = \frac{z_{2}}{d_{2}}} & (34) \\{\beta_{2} = {\tan^{- 1}\left( \frac{z_{2}}{d_{2}} \right)}} & (35)\end{matrix}$

Similarly, the sum z₂+l₂+r₂ is a known, measurable quantitycorresponding to the distance between the x-coordinate of position 716and the right edge of image 712. Furthermore, the distance z₂+l₂corresponds to the distance x₂ from FIGS. 7C and 7D.

The angle θ₂ may be derived, based on triangle 734, using Equation (36)and may be expressed according to Equation (37).

$\begin{matrix}{{\tan \left( {\beta_{2} + {2\; \theta_{2}}} \right)} = \frac{z_{2} + l_{2} + r_{2}}{d_{2}}} & (36) \\{\theta_{2} = {{\frac{1}{2}{\tan^{- 1}\left( \frac{z_{2} + l_{2} + r_{2}}{d_{2}} \right)}} - \frac{\beta_{2}}{2}}} & (37)\end{matrix}$

With angle θ₂ and β₂ known, the distance l₂ may be derived based onEquation (38) and expressed according to Equation (39).

$\begin{matrix}{{\tan \left( {\beta_{2} + \theta_{2}} \right)} = \frac{z_{2} + l_{2}}{d_{2}}} & (38) \\{l_{2} = {{d_{2}{\tan \left( {\beta_{2} + \theta_{2}} \right)}} - z_{2}}} & (39)\end{matrix}$

The distance r₂ may likewise be expressed according to Equation (40).Alternatively, since the sum z₂+l₂+r₂ is known, r₂ may be determinedarithmetically.

r ₂ =d ₂ tan(β₂+2θ₂)−z ₂ −l ₂  (40)

The angle α₂, as shown in FIGS. 7C and 7E, may be expressed according toEquation (41).

α₂=β₂+θ₂  (41)

This method of determining the angle α₂ may be used in combination withor in place of any of the methods described with respect to FIGS. 7C and7D.

The length f may be derived based on triangle 734 using Equation (42),where y is determined according to Equation (29).

$\begin{matrix}{{\cos \left( \alpha_{2} \right)} = \frac{d_{2}}{f + y}} & (42)\end{matrix}$

The length f may be expressed according to Equation (43).

$\begin{matrix}{f = {\frac{d_{2}}{\cos \left( \alpha_{2} \right)} - y}} & (43)\end{matrix}$

Consequently, the size a of object 702 may be expressed according toEquation (44) by combining Equations (33), (37), and (43).

$\begin{matrix}{a = {\left( {\frac{2d_{2}}{\cos \left( \alpha_{2} \right)} - y} \right){\sin \left( {\alpha_{2} - {\tan^{- 1}\left( \frac{z_{2}}{d_{2}} \right)}} \right)}}} & (44)\end{matrix}$

At this point, the size a may be computed numerically based on the knownor measurable quantities, according to Equation (44). The size a may beused to compute the magnification M₂ according to Equation (32).Alternatively or additionally, some embodiments may determine the levelof magnification for each half of the object of interest. Specifically,magnification of the left side M_(2l) of image 712 may be expressed asaccording to Equation (45).

$\begin{matrix}{M_{2l} = \frac{l_{2}}{a/2}} & (45)\end{matrix}$

Likewise, the magnification of the right side M_(2r) of image 712 may beexpressed according to Equation (46).

$\begin{matrix}{M_{2r} = \frac{r_{2}}{a/2}} & (46)\end{matrix}$

The magnification M₂ may be used to scale the image 712 in order toaccurately and proportionately represent the actual physical size a ofobject 702. Alternatively or additionally, the magnification M_(2l) maybe used to scale the left side of image 712, having length l₂, and themagnification M_(2r) may be used to scale the right side of image 712,having length r₂, in order to more accurately account for any elongationof image 712. The above procedure may also or instead be carried out forimage 710 corresponding to radiation source 700 at position 714.

FIGS. 8A and 8B illustrate yet another example embodiment fordetermining 3D information based on at least two 2D images acquired fromdifferent perspectives. FIG. 8A illustrates radiation source 800positioned above receiver 804 at position 814. The radiation source 800emits radiation 806, producing an image 810 of object 802 shown in thetop view 808A of receiver 804. An x-y coordinate frame attached to thetop view 808A indicates the spatial relationship between the receive 804and the object 802 at the moment that image 810 was captured. The image810 has a diameter e₁.

The radiation source is subsequently translated and rotated 90 degreescounterclockwise from position 814 to position 816, as indicated byarrow 820 in FIG. 8B. Similarly, the receiver 804 is rotated 90 degreesclockwise, as indicated by arrow 818, in order to receive the radiation806 from the rotated radiation source 800. The radiation 806 in FIG. 8Bis now directed perpendicular to the radiation 806 in FIG. 8A.

The bottom of the receiver 804 is positioned at the same height (alongthe z-axis) in both FIG. 8A and FIG. 8B. Namely, the receiver 804 isrotated, but not translated, between FIGS. 8A and 8B. A y-z coordinateframe attached to the top view 808B indicates the spatial relationshipbetween the receiver 804 and the object 802 at the moment that image 812was captured. The object 802 remains in the same position and at thesame height h in both FIGS. 8A and 8B. Accordingly, the height of thecenter of the object of interest h is equal to the height of the centerof projected image 812. This holds true when the radiation source 800 atposition 816 is at approximately the same height h as object 802. Thecase when radiation source 800 and object 802 are not aligned at thesame height h is discussed below. The height h can be determinedexplicitly based on image 812 using a computing device. The computingdevice may execute program instructions that cause the computing deviceto determine the center of image 812 and determine the distance betweenthe center of image 812 and the bottom (along the z-axis) of theradiograph containing image 812.

The height h may be used to determine the magnification M₁ of image 810according to Equation (6). The image 810 may be scaled according to thedetermined magnification M₁ so as to accurately represent the actual,physical size of object 802. Although FIGS. 8A and 8B depict theradiation source 800 centered with the object 802, alternativeembodiments may function when the radiation source 800 and object 802are not centered or aligned. When radiation source 800 and object 802are not aligned and centered, embodiments may determine the height h ofobject 802 by accounting for the exact geometric relationship betweenthe object 802, the radiation source 800, and receiver 804. Accountingfor the exact geometric relationship may comprise calculations similarto those presented with respect for FIGS. 7A-7E. Additionally, anyresulting image elongation may be accounted for or corrected using anyof the embodiments described with respect to FIGS. 7A-7E. In someembodiments, the impact of any misalignment between object 802 andradiation source 800 may be negligible and may be ignored.

VI. Determining Object Spatial Orientation

FIGS. 9A-9D illustrate an example embodiment enabling the determinationof the orientation of an object of interest. Specifically, FIG. 9Aillustrates an AP radiograph 900 of a human hip. The hip radiographcomprises images of acetabulum 902, femoral head 904, and femoral calcar906. The center of the acetabulum image 902 and the center of thefemoral head image 904 are indicated by a circular marker. The femoralcalcar image 906 is indicated by a triangular marker. The two markersare separated by a distance d. The distance d may be determined in theplane of the radiograph 900. A computing device may be programmed orconfigured to automatically detect the images 902, 904, and 906 andplace the markers in the appropriate position. Alternatively, a user maymanually place the markers at the appropriate location of the radiograph900 or a digital representation thereof using a graphical userinterface. The computing device may determine the distance d based onthe positions of the markers by, for example, counting the number ofpixels separating the markers.

FIG. 9B illustrates a cross table lateral hip radiograph 908 of the samehuman hip. The center of the acetabulum image 902 and the femoral calcarimage 906 are located at different heights, separated by a verticaldistance h, above the radiographic receiver. In FIG. 9A, the verticaldistance h (not illustrated) is coming out of the page. As a result, thefemoral calcar image 906 and the acetabulum image 902 have two differentmagnifications on the AP radiograph 900. A computing device may likewisebe programmed or configured to determine the distance h based on thepositions of the circular and triangular markers in radiograph 908 asdescribed above.

According to the methods described herein, the image of each object ofinterest may be scaled based on the level of magnification correspondingto the particular image. For example, the magnification of theacetabulum image 902 may be determined based on the height of theacetabulum above the radiographic receiver, using any of the embodimentsdescribed with respect to FIGS. 6A-8B. Similarly, the magnification ofthe femoral calcar image 906 may be determined based on the height ofthe femoral calcar above the radiographic receiver. For example,radiograph 900 may be a first of two AP hip radiographs. Radiograph 900may be used with a second AP hip radiograph (not illustrated) accordingto the embodiments described with respect to FIGS. 6A-7E to determinethe magnification of acetabulum image 902 by determining the height ofthe acetabulum and determine the magnification of the femoral calcar 906by determining the height of the femoral calcar.

Alternatively, radiographs 900 and 908 may be used together according tothe embodiment described with respect to FIGS. 8A and 8B to determinethe magnification of acetabulum image 902 and femoral calcar image 906.The height difference h may be determined based on any of theembodiments of FIGS. 6A-8B.

The acetabulum image 902 may be scaled based on its determinedmagnification to display the actual physical size of the acetabulum.Likewise, femoral calcar image 906 and femoral head image 904 may bescaled based on the determined, corresponding magnifications to displaythe actual physical size of femoral calcar and femoral head.Accordingly, the templating process may account for the differentmagnifications of the different anatomical features of the hip. Forexample, two or more templates may be used, each with a scaling factoraccurate for the specific object being measured (e.g. femoral calcar,femoral head, acetabulum). Some embodiments may apply the same scalingfactor to every object of interest determined to be at a particularheight. Some embodiments may comprise a computing device causing adisplay to show an object scaled according to its determinedmagnification, along with an unscaled template overlaid thereon.

Additionally, the methods described herein may allow the spatialorientation of an object to be determined based on the height of two ormore different points on or features of the object. For example, bydetermining the height of the femur head corresponding to image 904 andthe height of the femoral calcar corresponding to image 906, therotation of the femur may be determined. FIG. 9C illustrates an axialview (the transverse cross-sectional plane of the human body) of thehuman hip depicted in radiograph 900 of FIG. 9A and radiograph 908 ofFIG. 9B. The overlaid geometry illustrates how the measured distance dand the determined height difference h form a right triangle. The heightdifference h may be determined by calculating the difference between theheight of the femur head and the femoral calcar as previously described.FIG. 9D shows the overlaid geometry of FIG. 9C enlarged and modeled astriangle 910 labeled with the corresponding dimensions. Based ontriangle 910, angle ω may be expressed according to Equation (47) andangle ε may be expressed according to Equation (48) or, equivalently,according to Equation (49).

ω=sin⁻¹(h/d)  (47)

ε=90−ω  (48)

ε=cos⁻¹(h/d)  (49)

In the present example embodiment, the angles ω and ε may represent theextent of hip rotation. For example, angle ω may represent the extent offemoral anteversion. Angle ε may be an alternative way of representingfemoral version (twist). Alternative embodiments may determine thespatial orientation of other body parts or objects using the methodsdescribed herein. Some embodiments may acquire more than two images inorder to determine the spatial orientation in multiple reference planes.Example embodiments may determine the spatial orientation of multipleobjects present in the same image. For example, the degree of rotationof both hips may be determined at the same time, provided that theradiograph encompasses both hips.

The determined degree of hip rotation, or more generally, the determinedthree-dimensional spatial orientation of an object of interest, may beused in combination with templating techniques. Specifically, the objectof interest may be templated using templates that reflect the 3D spatialorientation of the object being measured. The templates may bethree-dimensional representations of prostheses and may be rotated intothat same 3D spatial orientation as the object in order to select aprosthesis closest in size and shape to the object. Alternatively, thetemplates may be two-dimensional and may comprise a plurality of imagesof the prostheses representing different spatial orientations of theprostheses.

In contrast, using a template that does not correspond to the spatialorientation of the object of interest may result in measurement errorbecause the shape of the image of the object may be significantlydifferent depending on the spatial orienting of the object during imageacquisition. For example, the shape of the image of the hip changessignificantly as the hip is rotated, as illustrated in FIGS. 10A-10D.FIG. 10A illustrates a radiograph 1000 of a human hip comprisingacetabulum image 1002, femoral head image 1004, and femoral calcar image1006. The radiograph 1000 is taken when the hip is at a neutral positionas illustrated by the axial view of the hip in FIG. 10B. Specifically,the line 1010, connecting the circular marker indicating the center ofthe head of the femur and the triangle indicating the femoral calcar, ishorizontal (parallel to the coronal plane of the human body). FIG. 10Cillustrates a second radiograph 1008 of the same human hip taken whenthe hip is rotated. The degree of rotation is illustrated in FIG. 10D byline 1014, showing the change from the original alignment of thecircular marker indicating the center of the head of the femur and thetriangle indicating the femoral calcar along line 1010 to the newalignment along line 1012. It may be observed that the anatomicalfeature image 1014 of the femur in radiograph 1000 looks different thananatomical feature image 1016 in radiograph 1008 due to the femur beingoriented (rotated) differently in the two images.

Consequently, using a template that does not reflect the same degree ofrotation as does the image of the hip may result in selection of a hipreplacement prosthesis that does not accurately match the anatomy of agiven patient. Determining the degree of hip rotation, as describedabove, allows for the selection of a template that corresponds to theimage of the hip at the given orientation. As a result, the process ofselecting a replacement hip prosthesis may be based on templates thataccurately reflect the orientation of the hip at the time of imageacquisition. Furthermore, the advantages of rotational templateadjustment, as described above, are not limited to hip and may beextended to any body part of interest. The techniques described hereinmay also be applied during radiographic imaging without the templatingprocess in order to produce a more accurate representation of theanatomical proportions of the objects of interest.

VII. Example Implementations Using a Calibration Marker

Existing approaches for determining image magnification require that amedical professional (e.g., a radiography technician) place a marker ofknown size at the same height as the object of interest. Such methodsrely on only one image of the object of interest. Since the marker andthe object of interest are at the same height, the magnification of theobject of interest should be the same as the magnification of themarker. Additionally, since the size of the marker is known, themagnification may be determined based on the ratio of the size of theimage to the actual size of the marker.

This method assumes that the marker was correctly placed at the heightof the object of interest, using proper technique by the medicalprofessional. When the marker is not placed correctly, the size of theobject of interest may be incorrectly determined, leading tocomplications. For example, in the case where the hip is being sized fora replacement prosthesis, determining the size incorrectly may lead tothe medical professional ordering incorrectly sized hardware and/orattempting to insert the incorrectly sized hardware during surgery. Theembodiments described herein eliminate the need for positioning acalibration marker at the same height as the object of interest.Instead, the marker may be placed at any height reasonably close to thatof the object of interest.

In automated radiography systems, human error associated withpositioning the radiation source and receiver is eliminated. Theembodiments described herein may accurately determine the size andorientation of the object of interest based an accurate record of therelative position between a radiation source and a radiation receiver atthe moment that a corresponding radiograph is captured. However, inradiography systems without automated position feedback systems, atechnician may manually determine and record the relative position ofthe radiation source and the receiver. Human error in positioning theradiation source and receiver, determining the relative position betweenthe radiation source and receiver, and/or recording the relativeposition between the radiation source and receiver may result in errorsin the determined image magnification which may in turn lead to surgicalcomplications.

The example embodiments that follow, in combination with the methodsdescribed above, may allow for the reduction or elimination of humanerror by using a calibration marker to determine the relative positionof the radiation source and the radiation receiver. Contrary to othermethods, the calibration marker may not need to be placed at the sameheight as the object of interest. Instead, the marker may be attached tothe radiation source or placed on the radiation receiver or radiationreceiver holder (e.g., patient table). The calibration marker methoddoes not require special equipment (aside from the marker itself).Additionally, the calibration marker approach described herein does notrequire additional staff training and/or testing and may be used withany radiation imaging apparatus.

In general, the calibration marker method may be used wheneverconsistent placement of the radiation source in relation to theradiation receiver is important. The marker itself may be made of anymaterial such that, under commonly used radiation intensities andexposure times, a clear image of the marker is produced on the radiationreceiver (otherwise called a radio dense material). The calibrationmarker may be used to identify and correct for errors in the placementof the radiation source and other human error. Specifically, thecalibration marker method may be used to accurately determine theposition of the radiation source relative to the radiation receiver insystems where that position is not automatically determined or wheremanual determination of the position may be subject to errors.Alternatively or additionally, the calibration marker may be used todetermine the difference between the known height of the calibrationmarker and an unknown height of the object of interest.

In general, the marker may have a known size and may be positioned at aknown position, vertical and/or horizontal, in relation to either thesource or receiver. Mathematically, the number of known variables withrespect to the size and/or position of the calibration marker may beequal to or greater than the number of independent equations describingthe position of the radiation source in relation to the receiver in aparticular geometric arrangement. As a result, the position of theradiation source in relation to the receiver may be determined based onthe known properties of the calibration marker. Specifically, the knownvariables may be any two of the set including the height of the markerabove the receiver or below the source, the horizontal position of themarker with respect to the receiver or the source, and the size of themarker.

FIG. 11 illustrates an example embodiment in which a calibration markeris used to determine the height of the radiation source. Radiationsource 1100 is positioned an unknown distance d above receiver 1104 andemits radiation 1106. The distance d may be unknown due to a lack ofmeans for measuring the distance accurately. Alternatively, the distancemay be uncertain in that it may have been inaccurately or erroneouslymeasured by a radiography technician. The calibration marker may be usedto determine, verify, and/or validate the position of the radiationsource 1100 in relation to receiver 1104.

Object of interest 1102, having an unknown size (diameter) a, andcalibration marker 1122, having a known size (diameter) m and positioneda known height h above the radiation receiver 1104, are exposed toradiation 1106. The calibration marker produces image 1124, having ameasurable size e, and the object 1102 produces image 1110, having ameasurable size i, as illustrated in the top view 1108 of receiver 1104.The calibration marker may be held at the fixed height h by a support1126 placed on the receiver 1104 or a receiver holder.

Using triangles 1118 and 1120, height d of radiation source 1100 may bederived by combining Equations (50) and (51), resulting in Equation(52).

$\begin{matrix}{{\tan (\theta)} = \frac{m/2}{d - h}} & (50) \\{{\tan (\theta)} = \frac{e/2}{d}} & (51) \\{d = \frac{eh}{e - m}} & (52)\end{matrix}$

With the height of the radiation source 1100 now known, themagnification of image 1110 of the object of interest 1102 may bedetermined according to any of the embodiments previously described.Alternative embodiments may use different spatial arrangements and/orgeometric models of the spatial arrangements of the source 1100, marker1122, and receiver 1104 in order to determine the position of theradiation source 1100 in relation to the receiver 1104.

FIG. 12A illustrates another example embodiment where the position ofthe radiation source in relation to the receiver is determined based onknown properties of the calibration marker. Similarly to FIGS. 7A-7C,two images of the calibration marker 1222 and the object of interest(not shown) may be taken using radiation source 1200 positioned abovereceiver 1204. The first image may be taken with radiation source 1200at position 1214, an unknown distance d₁ above the receiver 1204. Thehorizontal position, designated by line 1220, may also be unknown.Similarly, a second image may be taken with radiation source 1200 atposition 1216, an unknown distance d₂ above the receiver 1204. Thehorizontal position, designated by line 1218, may also be unknown. Aswith the embodiment of FIG. 11, the position of the radiation source1200 in relation to the radiation receiver 1204 may be unknown due to alack of means for measuring the distance accurately, uncertainty inmeasurements of the position, and/or erroneous measurements of theposition by a radiography technician. The calibration marker may be usedto determine, verify, and/or validate the position of the radiationsource 1200 in relation to receiver 1204. The calibration marker 1222may have a known size m, a known height h, and may be placed at a knownhorizontal distance in relation to the radiation receiver 1204.

The distance d₁ may be determined based on the magnification of themarker of known size m. Specifically, d₁ may be derived from Equation(53), where (e₁) is the size of the first image (image taken fromposition 1214, not shown) and where Equation (53) is a combination ofEquations (1) and (6).

$\begin{matrix}{M_{1} = {\frac{d_{1}}{d_{1} - h} = \frac{e_{1}}{m}}} & (53)\end{matrix}$

The distance d₁ may be expressed according to Equation (54).

$\begin{matrix}{d_{1} = \frac{e_{1}h}{e_{1} - m}} & (54)\end{matrix}$

Likewise, d₂ may be derived from Equation (55), where e₂ is the size ofthe second image (image taken from position 1216, not shown) and whereEquation (55) is a combination of Equations (2) and (8).

$\begin{matrix}{M_{2} = {\frac{d_{2}}{d_{2} - h} = \frac{e_{2}}{m}}} & (55)\end{matrix}$

The distance d₂ may be expressed according to Equation (56).

$\begin{matrix}{d_{2} = \frac{e_{2}h}{e_{2} - m}} & (56)\end{matrix}$

Some embodiments may remove and/or account for image elongation via anyof the methods previously discussed with respect to FIGS. 7A-7E.

The horizontal position of the radiation source 1200 at position 1214may be derived based on triangles 1228 and 1230. Specifically, the angleα₁ may be expressed according to Equation (57), where x₁ is the distancebetween the center of the image taken from position 1214 and thex-position of the calibration marker 1222.

$\begin{matrix}{\alpha_{1} = {\tan^{- 1}\left( \frac{x_{1}}{h} \right)}} & (57)\end{matrix}$

The distance y₁, corresponding to the distance between the center of thefirst image taken from position 1214 and the x-position of the radiationsource 1200 at position 1214 may be expressed according to Equation(58).

y ₁ =d ₁ tan(α₁)  (58)

Consequently, the spatial position of radiation source 1200 in relationto receiver 1204 may be determined based on known properties of thecalibration marker. The analogous procedure may be carried out fortriangles 1224 and 1226 to determine the distance y₂ according toEquation (59).

y ₂ =d ₂ tan(α₂)  (59)

With the spatial position of the radiation source 1200 in relation toreceiver 1204 known at both positions 1214 and 1216, the magnificationof the image of the object of interest (not shown) may be determined.The determined magnification may be used to scale the image of theobject of interest in order to determine the actual physical size of theobject of interest. The scaled image of the object of interest maysubsequently be used with digital templating methods to determine atemplate closest in size to the actual physical size of the object ofinterest.

In some example embodiments, the calibration marker may be disposed uponor placed on a radiation receiver housing, instead of being placeddirectly on the radiation receiver itself. Alternatively, thecalibration marker may be placed on a radiographic table next to orabove the radiation receiver housing. In some example embodiments, theradiation receiver housing may have a feature or structure on or inwhich a calibration marker may be placed or attached. For example, someradiation systems may comprise a radiation receiver in the form of anX-ray cassette. The X-ray cassette may be held by or housed in acassette holder. The calibration marker may be placed on the cassetteholder. However, in some radiography systems, the radiation receivermight fit imprecisely in the radiation receiver housing. For example,the radiation receiver housing may be slightly bigger than the radiationreceiver (e.g., the cassette holder may be bigger than the X-raycassette). The imprecise fit may allow the radiation receiver to movearound inside the radiation receiver housing. Consequently, since thecalibration marker may be placed on the radiation receiver housing or ona radiographic table, the position of the calibration marker in relationto the radiation receiver may undesirably change between acquisitions ofthe first radiograph and the second radiograph.

For example, a first radiograph may be captured on a first X-raycassette held in a cassette holder. The first X-ray cassette may beremoved from the cassette holder. The radiation source may be moved to asecond position and/or orientation with respect to the X-ray cassetteand/or the cassette holder. A second X-ray cassette may be inserted intothe cassette holder. However, due to an imprecise fit, the secondcassette may be in a slightly different position inside the cassetteholder than the first X-ray cassette. While the calibration marker mayremain in the same position in relation to the radiation receiverhousing, the calibration marker may be in a slightly different positionin relation to the radiation receiver itself (the second X-raycassette). Accordingly, calculations that assume that the calibrationmarker is in the same position in relation to the first radiationreceiver (first X-ray cassette) and the second radiation receiver(second X-ray cassette) may produce results containing calculationerrors.

In alternative embodiments, the radiation receiver may be an integralpart of the radiation receiver housing. For example, in radiographysystems where the radiation receiver is an electronic detector (e.g.,sensor array), the radiation receiver might not need to be changedbetween acquisitions of successive images. In such embodiments,placement of the calibration marker on the radiation receiver housing,positioning of the calibration marker with respect to the radiationreceiver housing, and/or attachment of the calibration marker to theradiation receiver housing may be equivalent to placement, positioning,and/or attachment of the calibration marker to the radiation receiveritself since the radiation receiver and the radiation receiver housingmay be precisely and firmly fitted and/or connected together.Alternatively, the calibration marker may be placed, positioned, and/orattached directly to the radiation receiver itself as opposed to theradiation receiver housing. For example, the calibration marker may beplaced, positioned, and/or attached directly to the electronic detectoras opposed to the housing of the detector. In embodiments utilizingX-ray film and/or X-ray cassettes, placement, positioning, and/orattachment of the calibration marker directly to the film or cassettemay be impossible, impractical, or inaccurate. Accordingly, FIG. 12Billustrates an example embodiment that may be used to account for animprecise fit of a radiation receiver inside of a radiation receiverhousing.

In particular, FIG. 12B illustrates a radiation source 1200 located atposition 1216 above radiation receiver 1204. Position 1216 may be adistance d above the radiation receiver 1204 and may correspond to anx-coordinate position represented by line 1218. Radiation receiver 1204may be housed in a radiation receiver housing 1236. The radiationreceiver 1236 may also be called a radiation receiver holder (e.g.,X-ray cassette holder). The radiation receiver 1204 may be smaller thanradiation receiver housing 1236, resulting in an imprecise fit of theradiation receiver 1204 in the radiation receiver housing 1236.Accordingly, there may be variation in how different radiographytechnicians or medical professionals position the radiation receiver1204 in radiation receiver housing 1236.

FIG. 12B additionally illustrates a first calibration marker 1232 and asecond calibration marker 1234 attached to or retained by a calibrationmarker support structure 1238. The calibration marker support structure1238 may be placed on, positioned with respect to, and/or attached tothe radiation receiver housing 1236 at a known position. For example,radiation receiver housing 1236 may have a special slot specificallydesigned to retain and/or attach to the calibration marker supportstructure 1238. However, this is not required. The first calibrationmarker 1232 may have a known diameter m₁ and may be located at a knownheight h₁ above the radiation receiver. The second calibration marker1234 may also have a known diameter m₂ and may be located at a knownheight h₂ above the radiation receiver. The calibration markers 1232 and1234 may be separated from each other by a known horizontal distance s.The calibration markers 1232 and 1234 may produce corresponding images1240 and 1242, respectively, as illustrated in the top view 1208 ofradiation receiver 1204.

An x-y coordinate frame is shown attached to the top view 1208 ofradiation receiver 1204. Variation in positioning of the radiationreceiver 1204 inside of the radiation receiver housing 1236 may includea variation in the y-coordinate position of the radiation receiver 1204and/or a variation in the x-coordinate position of the radiationreceiver 1204. Since the calibration markers 1232 and 1234 are locatedin a known position with respect to the radiation receiver housing 1238,variation in the position of the radiation receiver 1204 inside theradiation receiver housing 1236 may change the relative position betweenthe radiation receiver 1204 and the calibration markers 1232 and 1234.Under such conditions, an assumption or estimation of the location ofthe calibration markers 1232 and 1234 in relation to the radiationreceiver 1204 may be inaccurate and/or incorrect and may lead to aninaccurate determination of the magnification of the correspondingimages of an object of interest.

However, by using at least two calibration markers, as illustrated inFIG. 12B, the position of the radiation source 1200 in relation to theradiation receiver 1204 may be determined without assuming or estimatingthe position of the at least two calibration markers in relation to theradiation source 1204. Instead, determination of the position of theradiation source 1200 in relation to the radiation receiver 1204 may bebased on the known distance s between the two calibration markers.Specifically, the height d of the radiation source 1200 above radiationreceiver 1204 may be determined, as discussed previously, according toEquation (52) using either calibration marker 1232 and image 1240 orcalibration marker 1234 and image 1242. Alternatively, some embodimentsmay perform a redundant calculation using both calibration markers 1232and 1234 and corresponding images 1240 and 1242 in order to verify theresults against each other.

The embodiment illustrated in FIG. 12B may be modeled as illustrated inFIG. 12C. The example model illustrated in FIG. 12C may be used todetermine the position of radiation source 1200 in relation to radiationreceiver 1204 and avoid any error resulting from imprecise positioningof the radiation receiver 1204 inside radiation receiver housing 1236.In particular, Equations (60) and (61) may be written based on triangles1244 and 1246, respectively.

$\begin{matrix}{{\tan \left( \theta_{1} \right)} = \frac{p}{d - h_{1}}} & (60) \\{{\tan \left( \theta_{1} \right)} = \frac{w}{d}} & (61)\end{matrix}$

The distance z may be determined based on a radiograph containing theimages 1240 and 1242 by measuring the distances between the centers ofthe respective images. Alternative embodiments may utilize a geometricmodel where the distance z may be determined between the edges of images1240 and 1242. In some embodiments, the distance z may be determined bya computing device using known feature detection and image recognitionalgorithms such as, for example, the Hough circle transform. Equations(60) and (61) may be combined into Equation (62).

$\begin{matrix}{\frac{p}{d - h_{1}} = \frac{w}{d}} & (62)\end{matrix}$

Similarly, Equations (63) and (64) may be written based on triangles1248 and 1250, respectively, where distance p is the distance betweencalibration marker 1232 and the line 1218 representing the x-coordinateof the radiation source 1200.

$\begin{matrix}{{\tan \left( {\theta_{1} + \theta_{2}} \right)} = \frac{p + s}{d - h_{2}}} & (63) \\{{\tan \left( {\theta_{1} + \theta_{2}} \right)} = \frac{w + z}{d}} & (64)\end{matrix}$

Equations (63) and (64) may be combined into Equation (65).

$\begin{matrix}{\frac{p + s}{d - h_{2}} = \frac{w + z}{d}} & (65)\end{matrix}$

Equations (62) and (65) may be combined and used to determine thedistance w according to Equation (66).

$\begin{matrix}{w = \frac{{z\left( {d - h_{2}} \right)} - {sd}}{h_{2} - h_{1}}} & (66)\end{matrix}$

After determining d and w for the first orientation, a second radiographmay be acquired from a second orientation by changing the relativeposition between the radiation source 1200 and the radiation receiver1204. The position of the radiation source 1200 in relation to radiationreceiver 1204 in the second orientation may be determined in ananalogous manner. The determined positions of the radiation source 1200in relation to the radiation receiver 1204 in the two orientations maybe used to determine a magnification of an image of an object ofinterest (not shown) by determining the height of the object of interestabove the radiation receiver 1204 according to any of the embodimentsdescribed herein. For example, the magnification may be determined bymeasuring a size (e.g., dimension such as a diameter, width, length,etc.) of an image of an object of interest as discussed in detail withrespect to FIGS. 6A-7E. Alternatively, the magnification may bedetermined by measuring a distance between an anchor point and areference point on the image of the object of interest, as discussed indetail with respect to FIGS. 14C-14E.

FIGS. 13A and 13B illustrate how a calibration marker may be used todetermine the height and magnification of an object of interest bydetermining a difference between a known height of a calibration markerand an unknown height of the object of interest. In FIG. 13A, radiationsource 1300 is located at position 1314, an unknown distance d₁ abovereceiver 1304. Object of interest 1302, having an unknown size a andlocated at an unknown height h above the receiver 1304, may be exposedto radiation, producing image 1310 that has a known (measurable)diameter i₁, as illustrated in the top view 1308 of receiver 1304.Calibration marker 1322, having a known size m, may be positioned aknown height b above the receiver 1304 using support structure 1326.Calibration marker 1322 may also be exposed to radiation, producingimage 1324 that has a known (measurable) diameter e₁, as illustrated inthe top view 1308 of receiver 1304.

Radiation source 1300 may subsequently be moved from position 1314 toposition 1316, as indicated by arrow 1320 in FIG. 13B. Additionally, thereceiver 1304 may also be rotated as from the position shown in FIG. 13Ato the position shown in FIG. 13B. The radiation source 1300 may beseparated from radiation receiver 1304 by an unknown distance d₂. Theobject of interest 1302 and calibration marker 1322 may be exposed toradiation, producing images 1312 and 1318, respectively. Image 1312 mayhave a known (measurable) diameter i₂. Similarly, image 1318 may have aknown (measurable) diameter e₂. Coordinate systems (x-y in FIG. 13A andy-z in FIG. 13B) are shown attached to the top view 1308 to illustratethe 3D spatial relationship of the acquired images 1310, 1324, 1312, and1318.

The distances d₁ and d₂ may be determined according to Equations (67)and (68). Some embodiments may account for image elongation as shown bythe example illustrated with respect to FIGS. 7A-7E.

$\begin{matrix}{d_{1} = \frac{e_{1}b}{e_{1} - m}} & (67) \\{d_{2} = \frac{e_{2}b}{e_{2} - m}} & (68)\end{matrix}$

The vertical distance Δd between the image 1312 and image 1318 may bedetermined by manual or automated measurements. The distance may bemeasured from the center of image 1312 to the center of image 1318, asillustrated. For example, a user may be prompted by a computing deviceto select (e.g., by clicking, pointing, touching, or dragging a marker)the centers of images 1312 and 1318. In some embodiments, the computingdevice may be programmed to automatically determine the centers ofimages 1312 and 1318 and measure the distance Δd. Alternatively, thedistance may be measured from the bottom of image 1312 to the bottom ofimage 1318, provided that a meaningful height difference is determined.

Based on the vertical height difference Δd, the height h of the objectof interest 1302 may be expressed according to Equation (69).

h=b+Δd  (69)

In the present embodiment, only the height b and the size m of thecalibration marker 1322 need to be known in order to determine themagnification of the object of interest 1302. Alternative embodimentsmay produce elongated images of the object of interest and thecalibration marker and may account for the elongation in a manneranalogous to that previously discussed with respect to FIGS. 7A-7E.Regardless, with the height h now known, the magnification of the image1310 of object of interest 1302 may be determined according to Equation(6). The image 1310 may be scaled to represent the actual physical sizea of the object of interest, and the actual size a may be used incombination with digital templating techniques to select a templateobject closest in size to the object of interest.

Alternatively, the distance c between the calibration marker 1322 andreceiver 1304 as positioned in FIG. 13B may be known. The distance Δwmay be determined and used to compute the distance f according toEquation (70).

f=c+Δw  (70)

The distance f may be used to determine the magnification M₂ of image1312 according to Equation (71).

$\begin{matrix}{M_{2} = \frac{d_{2}}{d_{2} - f}} & (71)\end{matrix}$

The determined magnification M₂ may be used to scale the image 1312 torepresent the actual physical size of the object of interest 1302.

FIG. 14A illustrates an embodiment where a calibration marker may beattached to a radiation source or radiation source housing. Thecalibration marker may be used to correct for errors in radiographictechnique by solving for the exact position of the radiation sourcerelative to a radiation receiver. Radiation source 1400 is positioned atlocation 1414 above a radiation receiver 1404. The radiation beamprojected by radiation source 1400 may be adjusted, automatically ormanually, to a position directly perpendicular to radiation receiver1404. Two calibration markers 1402 and 1406 are attached to theradiation source 1400. FIG. 14B illustrates a scaled geometricrepresentation of the region surrounding the calibration markers 1402and 1406. Specifically, FIG. 14B illustrates that both markers have asize m and are offset by a known height h and a known horizontaldistance b from the radiation beam. The marker 1402 produces image 1408having a size e₁ (not shown) and marker 1406 produces image 1410 alsohaving a size e₁ (also not shown). The radiation source 1400 at position1414 is an unknown distance d₁ above the radiation receiver. Thedistance d₁ may be unknown or uncertain for any of the reasonspreviously described herein.

The calibration markers 1402 and 1406 may be used to determine thedistance d₁. Specifically, d₁ may be determined based on thetrigonometric relations of Equations (72) and (73).

$\begin{matrix}{{\tan \left( \alpha_{1} \right)} = \frac{b}{h}} & (72) \\{{\tan \left( \alpha_{1} \right)} = \frac{x_{1}}{d_{1}}} & (73)\end{matrix}$

Using these equations, the distance d₁ may be expressed according toEquation (74), where h and b are known and x₁ may be determined based onthe images 1408 and 1410.

$d_{1} = \frac{x_{1}h}{b}$

For example, an image representation of the entire radiation receiver1404, including images 1408 and 1410, may be digitized and processed insoftware to measure the distances x₁, x₂, and x₃ using known imageprocessing methods. Since the distance x₁ and the position x₂ of image1408 relative to the radiation receiver 1404 are known, the relativeposition x₁+x₂ between the radiation source 1400 and the radiationreceiver 1404 is also known.

The distance d₁ may alternatively be determined based on themagnification of images 1408 and 1410. Specifically, the magnificationM₁ of image 1408 may be expressed according to Equation (75).Accordingly, the distance d₁ may be expressed according to Equation(76).

$\begin{matrix}{M_{1} = {\frac{d_{1}}{h} = \frac{e_{1}}{a}}} & (75) \\{d_{1} = \frac{e_{1}h}{a}} & (76)\end{matrix}$

Some embodiments may carry out both calculations. Since both embodimentsare expected to provide the same result (embodiments may account forimage elongation), the redundant calculations may serve as a safety netto catch errors. Although not illustrated, an image of an object ofinterest may also be acquired at the same time as images 1408 and 1410are acquired. Consequently, the determined position of radiation source1400 in relation to radiation receiver 1404 may be used to determine themagnification or orientation of the object of interest via any of theembodiments described herein.

The radiation source 1400, radiation receiver 1404, and the calibrationmarkers 1402 and 1406 may be configured such that images produced by thecalibration markers 1402 and 1406 do not significantly overlap the imageof the object of interest. Alternatively, the images of the calibrationmarker may be acquired during a first exposure of the calibrationmarkers 1402 and 1406 to radiation from radiation source 1400. After thefirst exposure, the calibration marker may be moved out of the radiationfield or removed from the radiation source 1400 entirely. The object ofinterest may subsequently be placed between the radiation source 1400and the radiation receiver 1404 without changing the relative positionof the radiation source 1400 and the radiation receiver 1404. The imageof the object of interest may be acquired during a second exposure.

The radiation source 1400 may subsequently be translated from position1414 to position 1416 by a distance v. The marker 1402 may now producean image 1418 and marker 1406 may produce image 1420, separated fromeach other and from images 1408 and 1410 by distances y₁, y₂, and x₃ asshown in FIG. 14A. In a first embodiment, the distance v may beaccurately determined via direct measurement. For example, the radiationsource 1400 may include a ruler that can accurately track the horizontalposition of radiation source 1400. Additionally, the vertical positionof the radiation source 1400 may remain unchanged, resulting in thedistance d₂ being equal to the distance d₁. Consequently, the relativeposition between the radiation source 1400 and radiation receiver 1404may be determined via simple arithmetic. Specifically, with the relativeposition x₁+x₂ between the radiation source 1400 and receiver 1404 atposition 1414 already known, the horizontal position of location 1416may be determined by adding the distance v to the horizontal coordinateof position 1414 and may be expressed as x₁+x₂+v.

In a second embodiment, the distance v may be known but the distance d₂may have changed; the distance d₂ may be different from the distance d₁.Accordingly, the distance d₂ may be determined based on themagnification of image 1418 of marker 1402 or the magnification of image1420 of marker 1406 as previously described. Alternatively, the distancemay be computed based on the trigonometric relation of Equation (77) andmay be expressed according to Equation (78).

$\begin{matrix}{{\tan \left( {\beta + {2\alpha_{1}}} \right)} = \frac{v - x_{1} - x_{3}}{d_{2}}} & (77) \\{d_{2} = \frac{v - x_{1} - x_{3}}{\tan \left( {\beta + {2\alpha_{1}}} \right)}} & (78)\end{matrix}$

In a third embodiment, distances d₂ and v may both be unknown. Thedistance d₂ may be determined based on the magnification of the image ofeither marker 1402 or 1406 as previously discussed. The distance v maybe expressed by Equation (79), where y₃ is the only unknown quantitywhile all other variables can be determined explicitly based on theimages 1408, 1410, 1418, and 1420 or as previously described herein.

v=y ₃ +y ₁ +y ₂ +x ₃ +x ₁  (79)

Accordingly, y₃ may be derived from Equation (80) and expressedaccording to Equation (81).

$\begin{matrix}{{\tan \left( {\beta + {2\alpha_{1}}} \right)} = \frac{y_{3} + y_{1} + y_{2}}{d_{2}}} & (80) \\{y_{3} = {{d_{2}{\tan \left( {\beta + {2\alpha_{1}}} \right)}} - y_{1} - y_{2}}} & (81)\end{matrix}$

Similarly to prior embodiments, the distance v may now be computedexplicitly and added to the x-position of the radiation source 1400 atlocation 1414 to determine the x-position of the radiation source 1400at location 1416 in relation to radiation receiver 1404. The now knownrelative position may be used by any of the methods described herein todetermine the magnification and orientation of an object of interest.The image of the object of interest may be scaled and used in digitaltemplating methods to determine a template object closest in size to theobject of interest.

In general, more or fewer calibration markers may be used. For example,some embodiments may use three calibration markers attached to theradiation source 1400. Regardless of their number, the calibrationmakers may be arranged in a particular pattern that facilitatesidentification of the image corresponding to each calibration marker ina radiograph. Alternatively or additionally, the calibration markers maybe arranged in a way that simplifies the computation and/or calculationsinvolved in determining the relative position between radiation source1400 and radiation receiver 1404. Some embodiments may use bothcalibration markers attached to the radiation source 1400 as well ascalibration markers attached to the radiation receiver 1404.

Alternative embodiments may use multiple redundant calibration markersin order to reduce or eliminate errors by verifying and/ordouble-checking any calculations. An example embodiment may have acalibration marker attached in a known position relative to theradiation source 1400 and may determine the position of radiation source1400 in relation to radiation receiver 1404 based on the image of thecalibration marker in the corresponding radiograph. A second calibrationmarker may be attached in a known position relative to the radiationreceiver 1404. The image of the second calibration marker may also beused to determine the position of radiation source 1400 in relation toradiation receiver 1404 based on the image of the second calibrationmarker in the corresponding radiograph. When the two calculationsproduce significantly different results, a medical professional and/orcomputing device may require or suggest that the radiographs be takenagain in a more careful manner. Conversely, when the calculationsproduce the same result, the medical professional may be confident inthe accuracy of the procedure.

FIGS. 14C-14E illustrate an exemplary embodiment where a magnificationof an object of interest is determined based on measurements of adistance between a reference point in an image of the object of interestand an anchor point (another reference point). Specifically, themagnification is based on a first distance between a first referencepoint of an image of the object of interest contained in a firstradiograph and an anchor point in the first radiograph and further basedon a second distance between the first reference point of an image ofthe object of interest contained in a second radiograph and the anchorpoint in the second radiograph. The anchor point may be anotherreference point but is referred to herein as an anchor point in order todifferentiate it from a reference point in an image of the object ofinterest. The distinction will be made clear by way of the followingexample.

FIG. 14C illustrates a radiation source 1400 positioned at position1414, a distance d₁ above a radiation receiver 1404. Two calibrationmarkers, 1402 and 1406, may be attached to the radiation source 1400.The calibration markers 1402 and 1406 may create correspondingcalibration markers images 1408 and 1410. As shown in FIG. 14D, theimages 1408 and 1410 (shown surrounded by dotted circles for emphasis)may be contained in radiograph 1422 acquired using radiation source 1400at position 1414 in relation to radiation receiver 1404. A computingdevice may locate images 1408 and 1410 in the representation ofradiograph 1422 by, for example, comparing the color and/or brightnessof the pixels in the representation. For circular images, the computingdevice may look for groups of pixels that fit a model of a circle usingthe Hough Circle Transform algorithm. The images may 1408 and 1410 maybe separated by a distance 2x₁. Line 1424 connecting the images 1408 and1410 may be determined. A midpoint 1426 of the line may be determinedand may subsequently be used as an anchor point in determining themagnification of the object of interest, according to the presentexample embodiment.

A distance e₁ may be determined or measured between center point (anchorpoint) 1426 and a reference point 1428 on the image 1427 of the objectof interest. The object of interest may be a femoral calcar, as shown inFIG. 14D. In some embodiments, the object of interest may be anotheranatomical feature. FIG. 14E illustrates a different view of FIG. 14C(some elements not shown for clarity). Specifically, object of interest1430 (illustrated in FIG. 14C as the femoral calcar) is shown positioneda vertical distance h above radiation receiver 1404. Reference point1428 and anchor point 1426 are separated by a distance e₁.

The distance d₁ may be known from a position feedback mechanism of theradiography system that includes the radiation source 1400 and radiationreceiver 1404. Alternatively, the distance d₁ may be determined based onthe calibration marker images 1408 and 1410, as described with respectto FIG. 14A. The distance e₁ shown in FIGS. 14C and 14E may be used inthe same manner as the diameter and/or size of the image of the objectof interest as described in any of the other embodiments describedherein. The distance e₁ may be used to determine a height of the objectof interest and, based on the height, determine the magnification of theimage of the object of interest.

Specifically, by way of example, the magnification of the image 1427contained in radiograph 1422 and/or a second image of the object ofinterest contained in a second radiograph (not shown) may be determined.The second image may be acquired from a second orientation where thesecond orientation is achieved by moving the radiation source 1400 up ordown from position 1414 into a second position, as discussed withrespect to FIGS. 6A-6D. In the second orientation, the radiation source1400 may be located a distance d₂ above the radiation receiver 1404.

Calibration markers 1402 and 1406 may produce corresponding images and aline may be determined connecting the images. The line may have a length2x₂ and a midpoint of the line may be used as an anchor point in thesecond radiograph. The anchor point in radiograph 1422 and the anchorpoint in the second radiograph may coincide with the same underlyinganatomical feature depicted in the radiographs. Accordingly, the anchorpoint may be a stationary reference point that does not move relative toradiograph 1422 and the second radiograph. A second distance e₂ (notshown) may be measured between the anchor point in the second radiographand the reference point 1427 (reference anatomical feature) of thesecond image of the object of interest contained in the secondradiograph. Due to vertical movement of the radiation source in relationto the radiation receiver, the magnification of the second image of theobject of interest and the position of the second image of the object ofinterest will be different in the second radiograph than in the firstradiograph 1422. Accordingly, analogously to FIGS. 6A and 6B, thedistances e₁ and e₂ will be different.

The height h of the object of interest 1430 may be determined based ontriangles 1432 and 1434 illustrated in FIG. 14E. Specifically, based ontriangles 1432 and 1434, the tangent of the angle θ₁ may be expressed asEquations (82) and (83) respectively.

$\begin{matrix}{{\tan \left( \theta_{1} \right)} = \frac{b}{d_{1} - h}} & (82) \\{{\tan \left( \theta_{1} \right)} = \frac{e_{1}}{d_{1}}} & (83)\end{matrix}$

Equations (82) and (83) may be combined into Equation (84) to solve forb, where b is the distance between the edge (reference point) of objectof interest 1430 and a line projecting from the radiation source 1400 toanchor point 1426. The magnification M₁ of the image 1427 contained inradiograph 1422 may be expressed according to Equation (6).

$\begin{matrix}{{\frac{b}{d_{1} - h} = \frac{e_{1}}{d_{1}}}{b = \frac{e_{1}\left( {d_{1} - h} \right)}{d_{1}}}} & (84)\end{matrix}$

An equivalent procedure may be carried out for the second image acquiredwith the radiation source at the second position, as described withrespect to FIGS. 6A-6D. Based on the second image contained in thesecond radiograph, the distance b may also be expressed according toEquation (85) and the magnification M₂ of the image 612 may be expressedby Equation (8).

$\begin{matrix}{b = \frac{e_{2}\left( {d_{2} - h} \right)}{d_{2}}} & (85)\end{matrix}$

In order to determine the magnification of either image 1427 or thesecond image contained in the second radiograph, example embodiments maydetermine the height h of the object 1430 by combining Equations (84)and (85), resulting in Equation (86).

$\begin{matrix}{{\frac{e_{1}\left( {d_{1} - h} \right)}{d_{1}} = \frac{e_{2}\left( {d_{2} - h} \right)}{d_{2}}}{{e_{1}{d_{2}\left( {d_{1} - h} \right)}} = {e_{2}{d_{1}\left( {d_{2} - h} \right)}}}{h = \frac{d_{1}{d_{2}\left( {e_{2} - e_{1}} \right)}}{{d_{1}e_{2}} - {d_{2}e_{1}}}}} & (86)\end{matrix}$

The height h may now be used with Equations (6) and (8) to determine themagnifications M₁ and M₂. The determined magnifications may be used toscale the corresponding images in order to determine the actual physicalsize of the object of interest 1430. In general, any of the embodimentsdescribed herein may use a distance between an anchor point (stationaryreference point) and a reference point in an image of an object ofinterest in place of a diameter, size, or other dimension of the objectof interest when determining a height of the object of interest and/or amagnification of an image of the object of interest. The reference pointand/or anchor point may be any identifiable point in the radiograph andis not limited to the examples provided herein. The elements of theembodiment described with respect to FIGS. 14C-14E may be combined withany of the other embodiments described, illustrated, or otherwisecontemplated herein. Likewise, elements of all other embodimentsdescribed herein may be combined with the embodiment illustrated inFIGS. 14C-14E. The operations of the embodiment described with respectto FIGS. 14C-14E may be carried out by a computing device.

VIII. Example User Interface Implementations

The embodiments described herein may be implemented on a computingdevice. The computing device may be a computer executing programinstructions stored in a non-transitory computer readable medium or itmay be a device where the functions are implemented directly in hardwarecircuitry. In one embodiment, the computing device may also executeinstructions in order to provide a graphical user interface. Among otherfeatures, the graphical user interface may instruct a user to place avirtual marker at the position of the object of interest.

FIG. 15 depicts example user interface 1500 displaying a lateralradiograph of a human hip comprising acetabulum image 1502, femoral headimage 1504, and femoral calcar image 1506. The user interface 1500provides instructions 1512 to move the circle 1514 over the center ofthe femoral head image 1504. The example user interface may additionallyinclude buttons 1508 and 1450. For example, button 1510 may be used toinform the software that the circle 1514 has been placed over thefemoral head 1504. The user interface may subsequently prompt the userto identify other objects of interest, such as the femoral calcar image1506 or a calibration marker (not shown) if a calibration marker wasused.

Alternatively, the program instructions may cause the computing deviceto automatically identify all objects of interest via known feature(e.g., geometric feature) recognition algorithms. The automaticidentification of objects of interest may be indicated to a user viavirtual markers overlaid on top of the displayed radiograph. Forexample, circular marker 1514 may be shown overlaid atop the femoralhead image 1504 when the automatic identification of objects of interesthas been completed. The graphical user interface may prompt a user toverify and/or correct any errors committed by the automaticidentification process. The process of identifying the objects ofinterest may be repeated for all available radiographs.

The computing device may subsequently determine the height of theobjects of interest and the magnification corresponding to each objectof interest. If more than one object of interest is identified, thecomputing device may determine the spatial orientation of the objects ofinterest relative to each other. The computing device may scale theportions of the radiograph representing images of the objects ofinterest by the level of magnification corresponding to each object ofinterest. The scaled images may subsequently be used with digitaltemplating in order to determine a template closest in size to theactual physical size of the object of interest. For example, theacetabulum image 1502 in radiograph 1500 may be scaled according to thelevel of magnification determined to correspond to the acetabulum image1502. Since the femoral head is at the same height as the acetabulum(the femoral head is centered in the acetabulum and the two share thesame center point), templates representing replacement acetabularprostheses may be overlaid on top of the scaled acetabulum image 1502 tofind a replacement prosthesis closest in size and shape to the actualphysical size of the acetabulum represented by acetabulum image 1502.

Alternative embodiments may scale the template objects instead ofscaling the image of the object of interest. For example, a plurality oftemplate objects may represent a plurality of available replacement hipprostheses. Instead of scaling the image of the object of interest inorder to represent the actual physical size of the object of interest,the plurality of template objects may be scaled by the determined levelsof magnification of the objects of interest. The portion of the templatecorresponding to the femoral calcar image 1506 may be magnified by themagnification corresponding to the femoral calcar and the portion of thetemplate corresponding to the femoral head image 1504 may be magnifiedby the magnification corresponding to the femoral head. Alternatively,since the femoral head and the acetabulum form a concentricball-and-socket joint having the same center point, the two are locatedat the same height. Accordingly, the magnification determined tocorrespond to the femoral head image 1504 may, in this particularexample, also be used to scale the image of acetabulum 1502. Templatesmay be chosen from the plurality of templates that correspond to thedegree of rotation of the hip depicted in the radiograph. The rotationof the hip may be determined as previously described with respect toFIGS. 9A-9D. Consequently, the template object closest in size and shapeto the object of interest may be determined regardless of whether theimage or template is scaled.

FIGS. 16A and 16B illustrate another embodiment of a user interface. Theuser interface may display a radiograph 1600 of a human hip. Theradiograph 1600 may comprise acetabulum image 1602, femoral head image1604, and femoral calcar image 1606. Included in the radiograph may be acalibration marker image 1624. The user interface may display prompts1612-1616 requesting the placement of circle 1618 over the center of thefemoral head image 1604, triangle 1620 over the center of the femoralcalcar image 1606, and cross-hairs 1622 over the center of thecalibration marker image 1624. The shapes 1618-1622 may be varied amongimplementations. The user interface may additionally include a pluralityof buttons associated with different functions, such as, for example,button 1608 configured to cause the software to display additionalhelpful information and/or button 1610 configured to indicate to thesoftware that the tasks indicated by prompts 1612-1616 have beencompleted.

FIG. 16B illustrates an example state of the user interface from FIG.16A after the shapes 1618-1622 have been moved to their respectivepositions, as requested by prompts 1612-1616. Alternatively, thesoftware instructions may cause the computing device to move the shapes1618-1622 to their respective locations without user input. The softwareinstructions may cause the computing device to detect features ofinterest such as acetabulum image 1602, femoral head image 1604, andfemoral calcar image 1606 as well as calibration marker image 1624. Theanatomical feature images 1602, 1604, and 1606 may be detected usingknown feature detection algorithms.

The computing device may subsequently proceed to determine themagnification of the images of objects of interest 1602, 1604 and 1606,scale the images of the objects of interest 1602, 1604, and 1606according to the determined magnification, and/or determine theorientation of the femur relative to the pelvis (hip angle). The hipangle may be determined based on the height of the femoral head and thefemoral calcar, as discussed with respect for FIGS. 9A-9D. Thedetermined hip angle may be displayed on the user interface. Thedetermined magnifications corresponding to hip feature images 1602,1604, and 1606 as well as the determined hip angle may be used to find,via templating techniques, a prosthesis closest in size and shape to theanatomical features of the hip illustrated in radiograph 1600.

The templating process may comprise selecting a 2D template from aplurality of templates. The plurality of templates may represent 2Dimages and/or cross-sections of replacement hip prostheses of differentsizes and in different spatial orientations. The selected 2D templatemay correspond to the determined spatial orientation (hip angle) of thefemur in radiograph 1600 and may represent a prosthesis closest in sizeto the physical size of the anatomical features represented by images1602, 1604, and 1606 of the hip shown in radiograph 1600. Alternatively,a 3D template of the prosthesis may be rotated into the same orientationas the femur and may be used to template the hip or portions thereof.Some embodiments may use a 3D template to generate a plurality of 2Dtemplates. The template, portions of the template, radiograph, portionsof the radiograph representing the objects of interest, or a combinationthereof may be scaled according to the level of magnificationcorresponding to the objects of interest in order to determine atemplate closest in size to the actual physical size of the object orobjects of interest.

IX. Example Operations

FIG. 17 illustrates an example flow chart 1700. In block 1702, a firstradiograph, containing a first image of an object of interest may becaptured. The first radiograph may have been captured by a radiographicdevice with a radiation source and a radiation receiver in a firstorientation with respect to one another.

The radiograph may be in the form of a film (e.g., X-ray film) whenacquired using traditional radiography equipment. Alternatively, theradiograph may be a file or digital representation when acquired using aradiography system utilizing a digital radiation detector in place offilm. The representation of the radiograph may be the radiograph itself,a physical image copy of the radiograph, a digital image file, and/or atemporary display of the radiograph on a screen. For example, theradiograph may be represented and/or stored as a Joint PhotographicExperts Group file format (JPEG), Tagged Image File Format (TIFF),Graphics Interchange Format (GIF), Bitmap file format (BMP), PortableNetwork Graphics file format (PNG), or any number of other file types orfile formats. The object of interest may be a joint, a bone, a bonefeature, or any other object. For example, the object of interest may bethe head of a femur. The image of the object of interest may be an imagecreated on the radiation receiver when the object of interest is exposedto radiation from the radiation source.

In block 1704, the first radiograph may be stored along with metadatarepresenting vertical and horizontal positions of the radiation sourceand the radiation receiver in the first orientation. The metadata may beassociated with the representation of the radiograph. For example, themetadata may be stored as part of the file containing a representationof the radiograph. Alternatively, the metadata may be a separate filethat is linked to or associated with the file storing the representationof the radiograph.

In block 1706, at least one of the radiation source and the radiationreceiver may be moved so that the radiation source and the radiationreceiver are in a second orientation with respect to one another. Forexample, the radiation source may be translated horizontally, translatedvertically, and/or rotated with respect to the radiation receiver.Alternatively, the radiation receiver may be moved with respect to theradiation source. It may also be possible to move both the radiationsource and the radiation receiver relative to one another in order toplace them in the second orientation.

In block 1708, a second radiograph, containing a second image of theobject of interest may be captured or obtained. The second radiographmay be captured by a radiographic device with the radiation source andthe radiation receiver in the second orientation.

The first orientation may comprise, for example, position 614 ofradiation source 600 in relation to radiation receiver 604, as depictedin FIG. 6A. Similarly, the second orientation may comprise position 616of radiation source 600 in relation to radiation receiver 604, asdepicted in FIG. 6B. An alternative example of the first orientation maybe position 716 of radiation source 700 in relation to radiationreceiver 704, as depicted in FIG. 7B. Similarly, the second orientationmay alternatively comprise position 714 of radiation source 700 inrelation to radiation receiver 704, as depicted in FIG. 7A. The firstand second orientations may also be achieved according to any of theother example embodiments described herein. Additional orientations arepossible.

In block 1710, the second radiograph may be stored along with metadatarepresenting vertical and horizontal positions of the radiation sourceand the radiation receiver in the second orientation.

In block 1712, a magnification of the object of interest as representedby the first image or the second image may be determined. The determinedmagnification may be based on the captured radiographs and one or moreof the vertical and horizontal positions of the first and secondorientations. The magnification may be determined according to any ofthe example embodiments described herein. The operations of flow chart1700 may be carried out by a computing device, a radiographic system, ora combination thereof.

Determining a magnification of the object of interest according to block1712 may include determining a first width, dimension, and/or size ofthe first image and determining a second width, dimension, and/or sizeof the second image. Determining the magnification may also involvedetermining a vertical distance of the object of interest above theradiation receiver based on the first width, the second width, and oneor more of the vertical and horizontal positions of the first and secondorientations.

The object of interest may be, in general, any object, article, item, orfeature of interest. For example, the object of interest may be a boneor bone feature of a human body. The magnification determined in block1712 may be used to determine an unmagnified size of the object ofinterest. For example, the image of the object of interest contained ina radiograph or representation of a radiograph may be scaled and thescaled version may be saved, stored, and/or displayed. The unmagnifiedsize of the object of interest may be approximately equal to an actualphysical size of the object of interest. Based on the unmagnified size,a surgical template closest in size to the unmagnified size of theobject of interest may be selected from a plurality of surgicaltemplates of different sizes. For example, the surgical template mayrepresent a hip prosthesis that most closely matches the size and shapeof a patient's anatomical features of the hip. The plurality of surgicaltemplates may represent a range of the prostheses available off theshelf from different prosthesis manufacturers. The prosthesisrepresented by the selected surgical template may subsequently besurgically implanted to replace anatomical features of the patient.

In some embodiments, at least one of the first radiograph of block 1702and the second radiograph of block 1708 may additionally contain animage of at least one calibration marker having at least on knowndimension (e.g., width, diameter, height above or below the radiationsource or radiation receiver, position relative to the radiation sourceor radiation receiver). At least one of the vertical and horizontalpositions of the first orientation and vertical and horizontal positionsof the second orientation may be determined based on the image of the atleast one calibration marker and the at least one known property of theat least one calibration marker. This determination may be done inaccordance with any of the embodiments described with respect to FIGS.11-14B.

FIG. 18 illustrates another example flow chart 1800. In block 1802, arepresentation of a first radiograph, containing a first image of anobject of interest may be obtained. The first radiograph may have beencaptured by a radiographic device with a radiation source and aradiation receiver in a first orientation. The radiograph may be storedand/or represented in any of the formats previously discussed. Theradiograph or representation of the radiograph may be associated withmetadata indicating the positions of the radiation receiver and theradiation source.

In block 1804, a representation of a second radiograph, containing asecond image of the object of interest may be obtained. The secondradiograph may have been captured by a radiographic device with theradiation source and the radiation receiver in a second orientation. Thefirst and second orientations may be achieved according to any of theexample embodiments described herein. Additional orientations arepossible.

In block 1806, a vertical distance of the object of interest above theradiation receiver may be determined. The vertical distance may bedetermined based on a first width of the first image of the object ofinterest and a second width of the second image of the object ofinterest. The width may be any dimension of the image that isrepresentative of the size of the object or a portion thereof. Forexample, in the case of a circular object, the width may be a diameterof the circular image produced by the circular object. The verticaldistance of the object of interest above the radiation receiver may bedetermined according to any of the examples described herein.

In the first orientation, the radiation source and radiation receivermay be at a first vertical distance and a particular lateral distancefrom one another. In the second orientation, the radiation source andthe radiation receiver may be at a second vertical distance and at theparticular lateral distance from one another. The vertical distance ofthe object of interest above the radiation receiver may also be based onthe first vertical distance and the second vertical distance.Determination of the vertical distance of the object of interest abovethe radiation receiver may be done in accordance with the exampleembodiment of FIGS. 6A-6D.

The first vertical distance may be stored in first metadata associatedwith the representation of the first radiograph. Likewise, the secondvertical distance may be stored in second metadata associated with therepresentation of the second radiograph. The determination of thevertical distance of the object of interest above the radiation sourcemay further include obtaining the first vertical distance from the firstmetadata, obtaining the second vertical distance from the secondmetadata, obtaining the first width of the first image of the object ofinterest from the representation of the first radiograph, and obtainingthe second width of the second image of the object of interest from therepresentation of the second radiograph.

In an alternative embodiment, the radiation source and radiationreceiver may be at a first vertical distance and a first lateraldistance from one another in the first orientation. In the secondorientation, the radiation source and the radiation receiver may be at asecond vertical distance and at a second lateral distance from oneanother. The vertical distance of the object of interest above theradiation receiver may also be based on the first vertical distance, thefirst lateral distance, the second vertical distance, and the secondlateral distance. Determination of the vertical distance of the objectof interest above the radiation receiver may be done in accordance withthe example embodiment of FIGS. 7A-7E.

In some embodiments, at least one of the first radiograph of block 1802and the second radiograph of block 1804 may additionally contain animage of at least one calibration marker having at least on knowndimension (e.g., width, diameter, height above or below the radiationsource or radiation receiver, position relative to the radiation sourceor radiation receiver). At least one of the first vertical distance inthe first orientation, the first lateral distance in the firstorientation, the second vertical distance in the second orientation, andthe second lateral distance in the second orientation may be determinedbased on the image of the at least one calibration marker and the atleast one known dimension of the at least one calibration marker. Thisdetermination may be done in accordance with any of the embodimentsdescribed with respect to FIGS. 11-14B. Alternatively or additionally,the vertical distance of the object of interest may be determined basedon the image of the at least one calibration marker and the at least oneknown dimension of the calibration marker.

In additional embodiments, the vertical distance of the object ofinterest above the radiation receiver may also be based on the angles ofa triangle. The triangle may be formed by a first point within theobject of interest, a second point in the first image of the object ofinterest that is based on a first projection of the radiation sourcethrough the first point when the radiation source and the radiationreceiver are in the first orientation, and a third point in the secondimage of the object of interest that is based on a second projection ofthe radiation source through the first point when the radiation sourceand the radiation receiver are in the second orientation. Triangle 732illustrated in FIG. 7D may be an example of such triangle.

In further embodiments, the radiation source may be above andapproximately centered with respect to the radiation receiver in thefirst orientation. The radiation source may be off-center with respectto the radiation receiver by several centimeters (e.g., 5 centimeters),provided that this offset away from the center is accounted for in anycalculations of magnification or object height above the radiationreceiver. In the second orientation, the radiation source and theradiation receiver may be at the same horizontal level. The secondorientation may be achieved by rotation the radiation source and theradiation receiver by about 90 degrees from the first orientation. Forexample, the radiation source and the radiation receiver may be rotatedby anywhere from 80 degrees to 100 degrees. This range may be larger orsmaller provided that any calculations of magnification account for(include in the geometric model and associated calculations) the effectof the particular degree of rotation. This process may be done inaccordance with the embodiments described with respect to FIGS. 8A, 8B,13A, and 13B.

In block 1808, a magnification of the object of interest in one of thefirst radiograph or the second radiograph may be determined. Thedetermined magnification may be based on the vertical distance of theobject of interest above the radiation receiver. The magnification maybe determined according to any of the example embodiments describedherein. The operations of flow chart 1800 may be carried out by acomputing device, a radiographic system, or a combination thereof.

The determined magnification may be used to perform templatingoperations. For example, the object of interest may be a bone feature.Based on the determined magnification, an unmagnified size of the bonefeature may be determined. A surgical template may be selected from aplurality of surgical templates of different sizes. The selectedtemplate may be closest in size to the unmagnified size of the bonefeature.

The object of interest may be a first of many objects of interestrepresented by the radiograph. The first radiograph may additionallycontain a third image of a second object of interest. Likewise, thesecond radiograph may additionally contain a fourth image of the secondobject of interest. Based on the representation of the first radiograph,a horizontal distance between the first object of interest and thesecond object of interest may be determined in a plane of the firstradiograph. A vertical distance of the second object of interest abovethe radiation receiver may be determined based on a third width of thethird image and a fourth width of the fourth image. A height differencebetween the first object of interest and the second object of interestmay be determined based on the vertical distance of the first object ofinterest above the radiation receiver and the vertical distance of thesecond object of interest above the second radiation receiver. Athree-dimensional relationship between the first object of interest andthe second object of interest may be determined based on the horizontaldistance and the height difference between the first object of interestand the second object of interest.

In some embodiments, the first object of interest may be a first bonefeature of a bone and the second object of interest may be a second bonefeature of the bone. For example, the bone may be a femur. The firstbone feature may be the head of the femur and the second bone featuremay be the femoral calcar. Determining the three-dimensionalrelationship between the first bone feature and the second bone featuremay involve determining a degree of rotation of the bone. For example,the degree of rotation of the bone may be a degree of anteversion of thefemur measured with respect to the pelvis. The determination of thedegree of rotation of the bon may be done in accordance with theembodiment described with respect to FIGS. 9A-9D.

Based on the degree of rotation of the bone, a surgical template may beselected from a plurality of surgical templates. The plurality ofsurgical templates may have a plurality of different sizes and mayrepresent a plurality of three-dimensional orientations of replacementprostheses. For example, the plurality of surgical templates mayrepresent multiple two-dimensional cross-sections of a three-dimensionalprosthesis. Each cross-section may correspond to a different orientationof the three-dimensional prosthesis. Selecting a surgical template mayinvolve selecting a cross-section of the prosthesis that represents theprosthesis in approximately the same three-dimensional orientation asthe three-dimensional orientation of the bone at the time of capturingof the radiograph. The selected surgical template may be closest in sizeto a physical size of at least one of the first and second objects ofinterest. The selected surgical template may also be closest in shape tothe anatomical features of the bone and/or bone features.

In further embodiments, a particular image of the first image and thesecond image may be an elongated representation of the object ofinterest. Determining the magnification of the object of interest mayinclude determining a first magnification for at least a first portionof the particular image and determining a second magnification for atleast a second portion of the particular image. Based on the determinedfirst and second magnifications, an unmagnified size of the object ofinterest may be determined. A surgical template may be selected from aplurality of surgical templates of different sizes. The selectedsurgical template may be closest in size to the unmagnified size of theobject of interest. The first and second magnifications may bedetermined in accordance with the embodiments described with respect toFIGS. 7A-7E.

FIG. 19 illustrates another example flow chart 1900. Specifically, inblock 1902 a representation of a first radiograph containing a firstimage of an object of interest may be obtained. The first radiograph mayhave been captured by a radiographic device with a radiation source anda radiation receiver in a first orientation. In block 1904, arepresentation of a second radiograph containing a second image of anobject of interest may be obtained. The second radiograph may have beencaptured by a radiographic device with a radiation source and aradiation receiver in a second orientation.

In block 1906, a first distance between the first image and a referencepoint in the representation of the first radiograph may be determinedbased on the representation of the first radiograph. In block 1908, asecond distance between the second image and the reference point in therepresentation of the second radiograph may be determined based on therepresentation of the second radiograph. The operations of block 1906and 1908 may be carried out according the example embodiment describedwith respect to FIGS. 14C-14E.

In block 1910, a vertical distance of the object of interest above theradiation receiver may be determined. The determination of the verticaldistance may be based on the first distance and the second distance. Inblock 1912, a magnification of the object of interest may be determinedin one of the first radiograph or the second radiograph based on thevertical distance of the object of interest. The determinedmagnification may be used to scale the corresponding image in order toaccurately represent the actual physical size of the object of interest.Alternatively or additionally, the determined magnification may be usedin order to select a template object closest in size and/or shape to thesize and shape of the object of interest.

Flow charts 1700, 1800, and 1900 may be combined with any features,aspects, and/or implementations disclosed herein or in the accompanyingdrawings.

X. Conclusion

The present disclosure is not to be limited in terms of the particularembodiments described in this application, which are intended asillustrations of various aspects. Many modifications and variations canbe made without departing from its scope, as will be apparent to thoseskilled in the art. Functionally equivalent methods and apparatuseswithin the scope of the disclosure, in addition to those enumeratedherein, will be apparent to those skilled in the art from the foregoingdescriptions. Such modifications and variations are intended to fallwithin the scope of the appended claims.

The above detailed description describes various features and functionsof the disclosed systems, devices, and methods with reference to theaccompanying figures. The example embodiments described herein and inthe figures are not meant to be limiting. Other embodiments can beutilized, and other changes can be made, without departing from thescope of the subject matter presented herein. It will be readilyunderstood that the aspects of the present disclosure, as generallydescribed herein, and illustrated in the figures, can be arranged,substituted, combined, separated, and designed in a wide variety ofdifferent configurations, all of which are contemplated herein.

With respect to any or all of the message flow diagrams, scenarios, andflow charts in the figures and as discussed herein, each step, block,and/or communication can represent a processing of information and/or atransmission of information in accordance with example embodiments.Alternative embodiments are included within the scope of these exampleembodiments. In these alternative embodiments, for example, functionsdescribed as steps, blocks, transmissions, communications, requests,responses, and/or messages can be executed out of order from that shownor discussed, including substantially concurrent or in reverse order,depending on the functionality involved. Further, more or fewer blocksand/or functions can be used with any of the ladder diagrams, scenarios,and flow charts discussed herein, and these ladder diagrams, scenarios,and flow charts can be combined with one another, in part or in whole.

A step or block that represents a processing of information cancorrespond to circuitry that can be configured to perform the specificlogical functions of a herein-described method or technique.Alternatively or additionally, a step or block that represents aprocessing of information can correspond to a module, a segment, or aportion of program code (including related data). The program code caninclude one or more instructions executable by a processor forimplementing specific logical functions or actions in the method ortechnique. The program code and/or related data can be stored on anytype of computer readable medium such as a storage device including adisk, hard drive, or other storage medium.

The computer readable medium can also include non-transitory computerreadable media such as computer-readable media that store data for shortperiods of time like register memory, processor cache, and random accessmemory (RAM). The computer readable media can also includenon-transitory computer readable media that store program code and/ordata for longer periods of time. Thus, the computer readable media mayinclude secondary or persistent long term storage, like read only memory(ROM), optical or magnetic disks, compact-disc read only memory(CD-ROM), for example. The computer readable media can also be any othervolatile or non-volatile storage systems. A computer readable medium canbe considered a computer readable storage medium, for example, or atangible storage device.

Moreover, a step or block that represents one or more informationtransmissions can correspond to information transmissions betweensoftware and/or hardware modules in the same physical device. However,other information transmissions can be between software modules and/orhardware modules in different physical devices.

The particular arrangements shown in the figures should not be viewed aslimiting. It should be understood that other embodiments can includemore or less of each element shown in a given figure. Further, some ofthe illustrated elements can be combined or omitted. Yet further, anexample embodiment can include elements that are not illustrated in thefigures.

Additionally, any enumeration of elements, blocks, or steps in thisspecification or the claims is for purposes of clarity. Thus, suchenumeration should not be interpreted to require or imply that theseelements, blocks, or steps adhere to a particular arrangement or arecarried out in a particular order.

While various aspects and embodiments have been disclosed herein, otheraspects and embodiments will be apparent to those skilled in the art.The various aspects and embodiments disclosed herein are for purposes ofillustration and are not intended to be limiting, with the true scopebeing indicated by the following claims.

What is claimed is:
 1. A radiographic system comprising: a radiationsource; a radiation receiver, wherein at least one of the radiationsource and the radiation receiver is movable with respect to oneanother; a processor; a memory; and program instructions stored in thememory that, when executed by the processor, cause the radiographicsystem to perform operations comprising: capturing a first radiographcontaining a first image of an object of interest with the radiationsource and the radiation receiver in a first orientation with respect toone another, wherein a distance of the object of interest relative tothe radiation receiver is unknown; storing, in the memory, the firstradiograph and metadata representing vertical and horizontal positionsof the radiation source and the radiation receiver in the firstorientation; moving at least one of the radiation source and theradiation receiver so that the radiation source and the radiationreceiver are in a second orientation with respect to one another;capturing a second radiograph containing a second image of the object ofinterest with the radiation source and the radiation receiver in thesecond orientation; storing, in the memory, the second radiograph andmetadata representing vertical and horizontal positions of the radiationsource and the radiation receiver in the second orientation; and basedon the captured radiographs and one or more of the vertical andhorizontal positions of the first and second orientations, determiningthe distance of the object of interest relative to the radiationreceiver.
 2. The radiographic system of claim 1, wherein determining thedistance of the object of interest relative to the radiation receivercomprises: determining a first width of the first image; determining asecond width of the second image; and determining a vertical distance ofthe object of interest above the radiation receiver based on the firstwidth, the second width, and one or more of the vertical and horizontalpositions of the first and second orientations.
 3. The radiographicsystem of claim 1, wherein the program instructions further cause theradiographic system to perform operations comprising: based on thedetermined distance of the object of interest relative to the radiationreceiver, determining a magnification of the object of interest asrepresented by the first image or the second image.
 4. The radiographicsystem of claim 3, wherein the object of interest is a bone feature, andwherein the program instructions further cause the radiographic systemto perform operations comprising: based on the magnification of theobject of interest, determining an unmagnified size of the object ofinterest; and selecting, from a plurality of surgical templates ofdifferent sizes, a surgical template closest in size to the unmagnifiedsize of the object of interest.
 5. The radiographic system of claim 1,wherein determining the distance of the object of interest relative tothe radiation receiver comprises: determining a first distance betweenthe first image and a reference point in the first radiograph;determining a second distance between the second image and the referencepoint in the second radiograph; and determining a vertical distance ofthe object of interest above the radiation receiver based on the firstdistance and the second distance.
 6. The radiographic system of claim 5,wherein the reference point in the first radiograph comprises a midpointbetween a third image of a first calibration marker and a fourth imageof a second calibration marker, wherein the reference point in thesecond radiograph comprises a midpoint between a fifth image of thefirst calibration marker and a sixth image of the second calibrationmarker.
 7. The radiographic system of claim 1, wherein at least one ofthe first radiograph and the second radiograph additionally contains animage of at least one calibration marker having at least one knowndimension, and wherein the program instructions further cause theradiographic system to perform operations comprising: determining, basedon the image of the at least one calibration marker and the at least oneknown dimension of the at least one calibration marker, the vertical andhorizontal positions of the radiation source and the radiation receiverin the first orientation and the vertical and horizontal positions ofthe radiation source and the radiation receiver in the secondorientation.
 8. A method comprising: obtaining, by a computing device, arepresentation of a first radiograph containing a first image of anobject of interest, wherein the first radiograph was captured by aradiographic device with a radiation source and a radiation receiver ina first orientation, and wherein a vertical distance of the object ofinterest above the radiation receive is unknown; obtaining, by thecomputing device, a representation of a second radiograph containing asecond image of the object of interest, wherein the second radiographwas captured by the radiographic device with the radiation source andthe radiation receiver in a second orientation; and based on a firstwidth of the first image and a second width of the second image,determining, by the computing device, the vertical distance of theobject of interest above the radiation receiver.
 9. The method of claim8, wherein the radiation source and the radiation receiver are at afirst vertical distance and a particular lateral distance from oneanother in the first orientation, wherein the radiation source and theradiation receiver are at a second vertical distance and the particularlateral distance from one another in the second orientation, and whereinthe vertical distance of the object of interest above the radiationreceiver is also based on the first vertical distance and the secondvertical distance.
 10. The method of claim 9, wherein the first verticaldistance is stored in first metadata associated with the representationof the first radiograph, wherein the second vertical distance is storedin second metadata associated with the representation of the secondradiograph, and wherein determining the vertical distance of the objectof interest above the radiation receiver comprises: obtaining the firstvertical distance from the first metadata; obtaining the second verticaldistance from the second metadata; obtaining the first width from therepresentation of the first radiograph; and obtaining the second widthfrom the representation of the second radiograph.
 11. The method ofclaim 8, further comprising: based on the determined vertical distanceof the object of interest above the radiation receiver, determining, bythe computing device, a magnification of the object of interest in oneof the first radiograph or the second radiograph.
 12. The method ofclaim 11, wherein the object of interest is a bone feature, the methodfurther comprising: based on the magnification of the object ofinterest, determining an unmagnified size of the object of interest; andselecting, from a plurality of surgical templates of different sizes, asurgical template closest in size to the unmagnified size of the objectof interest.
 13. The method of claim 11, wherein a particular image ofthe first image and the second image is an elongated representation ofthe object of interest, and wherein determining the magnification of theobject of interest comprises (i) determining a first magnification forat least a first portion of the particular image and (ii) determining asecond magnification for at least a second portion of the particularimage, wherein the method further comprises: based on the first andsecond magnifications, determining an unmagnified size of the object ofinterest; and selecting, from a plurality of surgical templates ofdifferent sizes, a surgical template closest in size to the unmagnifiedsize of the object of interest.
 14. The method of claim 8, wherein theradiation source and the radiation receiver are at a first verticaldistance and a first lateral distance from one another in the firstorientation, wherein the radiation source and the radiation receiver areat a second vertical distance and a second lateral distance from oneanother in the second orientation, and wherein the vertical distance ofthe object of interest above the radiation receiver is also based on thefirst vertical distance, the second vertical distance, the first lateraldistance, and the second lateral distance.
 15. The method of claim 14,wherein the vertical distance of the object of interest above theradiation receiver is also based on the angles of a triangle formed by(i) a first point within the object of interest, (ii) a second point inthe first image of the object of interest that is based on a firstprojection of the radiation source through the first point, theradiation source and the radiation receiver in the first orientation,and (iii) a third point in the second image of the object of interestthat is based on a second projection of the radiation source through thefirst point, the radiation source and the radiation receiver in thesecond orientation.
 16. The method of claim 8, wherein at least one ofthe first radiograph and the second radiograph additionally contains animage of at least one calibration marker having at least one knowndimension, wherein the radiation source and the radiation receiver areat a first vertical distance and a first lateral distance from oneanother in the first orientation, wherein the radiation source and theradiation receiver are at a second vertical distance and a secondlateral distance from one another in the second orientation, and themethod further comprising: determining, based on the image of the atleast one calibration marker and the at least one known dimension of theat least one calibration marker, at least one of the first verticaldistance in the first orientation, the first lateral distance in thefirst orientation, the second vertical distance in the secondorientation, and the second lateral distance in the second orientation.17. The method of claim 8, wherein at least one of the first radiographand the second radiograph additionally contains an image of at least onecalibration marker having at least one known dimension, and wherein thevertical distance of the object of interest above the radiation receiveris further based on the image of the at least one calibration marker andthe at least one known dimension of the at least one calibration marker.18. A non-transitory computer readable medium having stored thereoninstructions that, when executed by a processor, cause the processor toperform operations comprising: obtaining a representation of a firstradiograph containing a first image of an object of interest, whereinthe first radiograph was captured by a radiographic device with aradiation source and a radiation receiver in a first orientation,wherein a vertical distance of the object of interest above theradiation receiver is unknown; obtaining a representation of a secondradiograph containing a second image of the object of interest, whereinthe second radiograph was captured by the radiographic device with theradiation source and the radiation receiver in a second orientation;determining, based on the representation of the first radiograph, afirst distance between the first image and a reference point in therepresentation of the first radiograph; determining, based on therepresentation of the second radiograph, a second distance between thesecond image and the reference point in the representation of the secondradiograph; and based on the first distance and the second distance,determining the vertical distance of the object of interest above theradiation receiver.
 19. The non-transitory computer readable medium ofclaim 18, wherein the operations further comprise: based on the verticaldistance of the object of interest above the radiation receiver,determining a magnification of the object of interest in one of thefirst radiograph or the second radiograph.
 20. The non-transitorycomputer readable medium of claim 19, wherein the reference point in therepresentation of the first radiograph comprises a midpoint between athird image of a first calibration marker and a fourth image of a secondcalibration marker, wherein the reference point in the representation ofthe second radiograph comprises a midpoint between a fifth image of thefirst calibration marker and a sixth image of the second calibrationmarker.